Prepared: September, 2003
Corn (Zea mays L.) defines agriculture in the Midwestern United States. With approximately 70 million acres in annual production and average per acre yields of 128 bushels per acre, the Midwestern states produce 90% of the 9-10 billion bushels of annual U.S. production. The importance of corn, not only to the United States but to the world, as a predominant feed and industrial grain cannot be overstated. While agricultural production is expanding worldwide as virgin grasslands and forests are converted to agriculture, the vast majority of this new production is incapable of supporting corn production.
The Midwestern United States represents the largest contiguous agro-ecosystem in the world capable of supporting corn production. U.S. Corn Belt agriculture produces 19 billion dollars of farmgate income annually with additional value derived from meat production, ethanol, sweeteners, industrial by-products, and other uses. Field corn production, therefore, is inextricably intertwined with the quality of life and economic well being and security of the Midwest. The businesses and support system of the communities within this region are closely linked to the agricultural sector and there is seldom a pain felt by the farmer that is not perceived by the farm community with equal impact. Nearly every local industry or service, from schools to banks to department stores, is tied to farm economics. A failure in the farm sector, in particular a failure in corn production, means a loss of income, businesses, and jobs throughout all communities. With profit margins at historic lows, producers are looking for opportunities to reduce the costs and risks of corn production to maintain their economic viability.
General Production Facts
Approximately 70 million acres of corn are grown in the North Central States (see Table 1) with a farmgate value of $19 billion annually. To growers in this area corn is a staple grain and feed crop. In fact, almost all tillable fields in this region, except the driest parts of KS, NE, SD and ND, will have corn grown on it from time to time.
In areas with concentrated dairy, beef, or hog production, corn is primarily used for feed grain. In areas more remote from livestock industries, corn may be processed for oil, sweeteners, and corn meal or shipped to domestic feed grain or export markets. Corn may be ensiled, but such use is primarily in areas where dairy or beef cattle are fed. Approximately 60 percent of all corn is consumed by livestock and the remaining 40 percent is processed for use by humans.
Although seed corn production is not specifically covered in this document there are many similarities between the pests and pest control measures used to control them. There are some significant differences, however, as inbred lines tend to be more susceptible to many pests and the higher value of the crop can justify greater pesticide use.
Throughout the Midwest, corn fields are closely managed and there is a general lack of tolerance for pests by producers. This lack of tolerance is often exacerbated by the level terrain of much of the Corn Belt and the ease with which uneven stands or weeds can be seen from the field's edge.
Table 1. Corn for Grain: Area Harvested, Yield, and Production by State and United States, 2000 and Forecasted October 1, 2001.
| 2001 | 2002 | 2001 | 20002 | 2001 | 2002 | ||
| State | Rank |
1,000 Acres |
--Bushels-- |
- 1,000 Bushels - | |||
| IL | 2 | 10,750 | 11,300 | 149 | 138 | 1,601,750 | 1,559,400 |
| IN | 5 | 5,750 | 5,670 | 160 | 117 | 920,000 | 616,590 |
| IA | 1 | 11,500 | 11,400 | 141 | 159 | 1,621,500 | 1,904,000 |
| KS | 8 | 3,100 | 2,600 | 132 | 110 | 409,200 | 286,000 |
| KY | 13 | 1,107 | 1,060 | 142 | 101 | 156,200 | 107,060 |
| MI | 11 | 1,950 | 2,090 | 92 | 117 | 179,400 | 244,530 |
| MN | 3 | 6,200 | 6,800 | 129 | 156 | 799,800 | 1,060,800 |
| MO | 10 | 2,570 | 2,700 | 136 | 100 | 349,520 | 270,000 |
| NE | 4 | 7,900 | 7,600 | 138 | 122 | 1,090,200 | 927,200 |
| ND | 12 | 660 | 705 | 110 | 110 | 72,600 | 113,300 |
| OH | 9 | 3,150 | 2,890 | 143 | 96 | 450,450 | 277,440 |
| SD | 7 | 3,400 | 3,500 | 116 | 95 | 394,400 | 332,500 |
| WI | 6 | 2,600 | 2,800 | 128 | 130 | 332,800 | 364,000 |
| US | 69,191 | 70,541 | 136 | 128 | 9,429,543 | 9,029,248 | |
Source: http://jan.mannlib.cornell.edu/reports/nassr/field/pcp-bb/2002/crop1102.txt
Current Cultural Practices
Corn is typically grown in a rotation with soybeans and less often with wheat, sorghum, or alfalfa. About 30 percent of the corn in the Midwest is grown as continuous corn. Planting may begin as early as mid March in the southern areas of the Corn Belt and the middle of May in northern areas, such as Minnesota and North Dakota.
No-till is practiced on about 20 percent of the corn acreage annually, and some form of conservation tillage practiced on another 20 to 30 percent. Because many producers feel that pest control measures tend to be less effective when corn is no-till planted, the use of no-till for field corn has not appreciably increased for several years. About 30 percent of the acreage is cultivated with a row cultivator and an estimated 30 percent is rotary hoed annually.
Approximately half of all pesticides are applied by the farmer and the other half are applied by commercially licensed dealers and applicators. In general there is a trend for larger farmers to apply a greater proportion of their own herbicides than would producers with small farms.
Approximately 90% of insecticides used on field corn are for soil insects and are applied by the farmer at planting with planter box applicators. The use of insecticidal seed treatments, as well as the use of liquid formulation insecticides, is becoming more common. Fungicide use is generally limited to the seed treatments that have been applied prior to purchase.
Earlier Planting
Cool soils (<50 degrees F @2" depth) during early season planting favors a high incidence of seedling diseases and a concomitant need for effective and low cost fungicides. Early planting also tends to shift weed populations toward weeds adapted to grow in cooler temperatures; lambsquarters, mustards, and smartweed species. The impact of several insect pests may also increase in earlier plantings.
Though planting later in the season is mentioned as a pest control strategy for many of the pests listed in this document, this may not be a practical solution for producers who must take advantage of 'windows of opportunity' to till and plant fields. A delay of a few days typically will result in yield reductions and can, in some years where weather is erratic, result in total crop failure. In order to capitalize on the advantages of early planting, pests must be controlled.
Use of Hybrids with GMO Traits
The use of hybrids for herbicide resistance or that express insect toxins is expected to increase, resulting in reductions in the pesticides used. Pest populations will also shift in response to the changes in herbicide and insecticide use. Overall, fields planted to varieties of corn with GMO traits are expected to have fewer weed and insect problems. An undesirable impact of this is that GMO use will raise the general standard for field cleanliness and appearance, and can result in an attitude among growers that will foster unnecessary pesticide use.
As more GMO crops are grown, and as multiple traits are 'stacked' in hybrids, there is an increasing likelihood of confusion for growers regarding what pesticides and pesticide resistance management strategies are necessary and sufficient. This trend is likely to further enhance the role of the professional in prescribing and applying pesticides.
In 2001, with over 30 percent of all corn bearing at least one GMO trait, the marketability of this grain has come to be a significant concern of nearly all farmers who grow corn for grain. However, many producers are looking to ethanol production, because it is not consumed by humans, as a means of avoiding some of this controversy.
Use of Conservation Tillage
The Conservation Tillage Information Center (CTIC) estimates that an average of 37% of corn acres are grown under some type of conservation tillage. These estimates have been relatively steady for the past five years. However, the perception that no-till corn acres are declining, especially in the eastern portion of the Corn Belt, is prevalent. Many of the reasons were pest related. Poor stands in no-till are attributed to cool wet soils which result in a greater risk for seed decay, seedling diseases, soil insect injury, and higher weed control costs. Undisturbed soil and the presence of crop residue results in more perennial weeds, the predominance of small seeded grass and broadleaf weeds, and a protective environment for many injurious insects. These trends require an effective array of soil-applied and burn-down herbicides as well as efficacious insecticides with sufficient persistence to adequately control soil-dwelling insects. Burn-down herbicides and herbicides that persist in the soil for the 6 to 8 weeks necessary to prevent weeds from competing with the crop during establishment, will remain a high priority.
Larger Farms
The size of farming operations continues to increase. Large farms operated by a single operator require the use of efficient technologies. Wherever practical, herbicides will continue to replace time-consuming pest management practices such as tillage and row cultivation. Growers will also continue to select technologies and products that allow for single-pass weed control or otherwise reduce the need for multiple trips through the fields. This suggests a continuing preference for pre-mixes and tank-mixes with broad spectrums of control and wide application windows. Larger farms also suggest that more decisions will be turned over to professional agronomists; either those working as dealers and distributors of ag-chem products or to private consultants.
More Landlord/Tenant Operations
The trend toward farm ownership being passed to those that do not directly operate them is expected to continue. Farmers will compete for available rental farmland and pressure will prevail to maintain high levels of pest control based more on aesthetics and perceptions than on economic thresholds. As a result, the use of pesticides for pest control will become further decoupled from threshold-based treatment levels. The expected outcome is that post emergence herbicide applications will remain in high demand for field cleanups. Keen competition for 'cash rent' land is also resulting in growers searching for ways to maintain input costs at low levels. Inexpensive pesticides provide growers with the tools necessary to maintain profitability.
Crop Scouting
Crop scouting is expected to increase slowly but steadily. Passage of the Farm Security and Rural Investment Act of 2002 is expected to provide incentives for farmers and landlords to adopt practices such as crop scouting. Farms that adopt professional crop scouting services are not likely to see immediate reductions in pesticide use, but rather are expected to benefit by having higher yields and lower pesticide expense as pests are managed more effectively in the long run. Many tenant farmers have been reluctant to make such an investment in the past because crop scouting is seen as an outlay of cash without an immediate return.
Pest Resistance
The number and severity of pests that have resistance to some pesticides will grow. This is a result of the repeated use of products that contain similar modes of action and the failure of many growers to observe recommended procedures for avoiding pest resistance. As new instances of pest resistance occur there is a continuing need for a broad array of pesticides with different modes of action, even if many of these chemicals are restricted to an emergency-use-only basis. The discovery of corn rootworms with extended diapause, although not strictly a pest resistance issue, and also corn rootworms that prefer to lay eggs in non-corn crop fields, are likely to affect pesticide use habits. Although the actual presence of rootworms with extended diapause in a corn field is expected to require insecticide use, the fear of having or getting the pest may cause additional insecticide use, much of which may be unwarranted.
Professional Pest Management and Pesticide Application Services
More growers are relying on commercial dealers and applicators to select and apply herbicides. Along with this trend comes the knowledge, skill, and latest technological techniques for accurate and effective application of pesticides. The number of corn acres managed by independent crop consultants and farm management services are increasing. The Certified Crop Advisor program, and the potential for their designation as third-party vendors, presents a unique opportunity for a significant increase in the use of professional pest management services.
The Biologic and Economic Importance of Pests in Field Corn
A somewhat quantitative measure of pest severity and impact can be found in Appendices E through H. Appendix E, F, and G provide an ordinal ranking of pests as determined through one of three separate means during the mid 1990's; a survey of scientists, a survey of growers, and an evaluation of the occurrence of pests (weeds only) from crop scouting records. These methods are admittedly based on perception of the problem more than their actual impact.
Appendix H provides an overview of losses caused by weeds, insects, and plant diseases as estimated by University discipline specialists. This information was collected in 1997 through interviews of specialists throughout the Corn Belt who were familiar with corn production. Though the data are also biased by the perceptions of individuals, the estimates are tempered by research experience and constant interaction with colleagues who have carefully studied each pest. At the beginning of each interview each specialist was asked to provide estimates for the pests thought most significant to corn production within each state. Because the term 'significant' is quite subjective, fewer pests were mentioned by some state specialists than others. Hence, these figures should be construed to be conservative in their estimates of losses as they do not thoroughly cover many "less important" pests.
The table in Appendix H presents the percent of acreage treated for each pest, the percent of acreage that remained above a threshold level after treatment, and the amount of loss resulting from treatment failure or lack of controls. Please note that the estimated losses include only the yield or quality reduction and do not include the cost of controls applied, whether the pest was controlled or not.
Losses for the pest categories of weeds, insects and diseases ranged from $17 to $23 per acre with losses due to weeds lowest and losses due to plant diseases the highest. Losses due to insects averaged about $20 per acre for the Corn Belt. The overall message conveyed by the specialists was that the more visible the pest, the greater likelihood of its treatment and a resultant reduction in its impact. For example, plant pathologists often indicated that producers may be unaware of many serious diseases or at least unable to respond in time to effectively control or manage them. Hence, their estimate of crop loss was very significant for some less visible diseases. Adding these losses suggests that producers still lose approximately $60 per acre per year due to the effects of pests in field corn.
The additional costs of control, to include improved seed, tillage, pesticides, and application costs can quickly increase these loss figures. Outside of the cost for improved seed, the cost of fungicide is minimal, probably less than one dollar per acre in most years. Cost of insecticides where used, can average $12 to $16 per acre. Current estimates suggest that insecticides may be used on about one third of the corn acreage in the Corn Belt, giving an average cost of from $4 to $6 dollars per acre of corn grown. This does not factor in the technology costs of improved Bt seed, where used. The cost for herbicides regularly exceeds $20 per acre and, since nearly all corn acres are treated with a herbicide, this figure is nominal for every acre. To these figures can be added the costs of pesticide application ($6 to $7 per acre) and the cost of tillage ($12-$20 per acre). These costs result in an average expenditure for pest management practices exceeding $50 for every acre of corn produced. Adding this cost to the estimate of losses for pests as indicated in the paragraph above, results in a very significant $110 per acre annual pest management expense, or roughly 8 billion dollars per year for the Corn Belt. For a complete enterprise analysis of corn production please see http://www.ers.usda.gov/Data/CostsAndReturns/testpick.htm
The following sections of this document cover the pests that are most problematic for field corn production in the Corn Belt as determined by the producers who participated in the Strategic Planning Workshops. At the beginning of each section is a brief overview of each pest category (insects, weeds, diseases) and some of the challenges faced by producers using chemical or non-chemical control strategies. Material that follows presents background information on the pest or pest group, some information relative to its importance as a pest to field corn, and some of the factors that affect its severity. Pesticides and non-chemical controls that are available for a pest are listed, along with any limitations or other restrictions that may affect proper or necessary control of the pest.
The use of conservation tillage practices, which leaves crop residue on the soil surface and reduces or eliminates the use of tillage, provides a protective environment for soil inhabiting insects, and may result in greater insect injury to the corn crop than does conventional tillage practices. It is also true that weeds and grasses present in no-till fields prior to planting are attractive egg laying sites for black cutworms which, when the larvae hatch, will move onto the corn. Although many predatory and beneficial insects are also favored by conservation tillage, the increase in such practices is in part responsible for some increases in the severity of some insect problems.
The severity of wireworms and white grubs is also tied to tillage practices and field cleanliness. No-till fields and fields that are excessively weedy are environments which foster the development of these insects. In general, regular herbicide use has improved field cleanliness, and weedy environments which promote white grub and wireworm activity are becoming very localized.
Very dry or drought conditions may reduce the impact of some insects while others may flourish. Spider mites are particularly problematic when dry weather is sustained. Under such conditions these pests are less likely to be held in check by natural diseases or predators and may cause severe crop injury. Grasshoppers and chinch bugs are often more common in drought years.
Whether insect control measures are used, and which treatments are selected, depends greatly on the economics of corn production. Low corn prices, production systems with lower yield potential (e.g. rainfed corn in western Corn Belt regions), and/or the failure to recognize that a pest is doing significant damage to the crop reduce the producer's inclination to treat for pests.
Producers often select insecticides in expectation of controlling multiple pests in the same field, or a later emerging insect that may be expected to occur soon after the original target pest has been identified. In such situations, insecticides may not be selected for their specificity to one insect, but more for its ability to control two or more insects within a complex.
Most producers now have a basic understanding of how unwise use of insecticides can select for resistance in insect populations. The wide range of management options available to producers has permitted them to minimize the development of insect resistance. However, the recent appearance of corn rootworms that have developed methods of circumventing the cultural practices that have traditionally been used for their control (crop rotation), is a cause for much concern. More effort is needed to determine a 'systems' approach to these pests and then educate producers and applicators on the proper choices and techniques for managing the development of resistance.
Though there appears to be a sufficient number of insecticide products and insecticide classes available for most major corn pests, it is deemed essential that this wide selection of products continue to be available to producers to provide a backstop for resistance management programs.
It is also important to understand that many of the following insect pests, though classified as 'moderate' or 'minor' importance to field corn production, can be very serious pests in localized areas, and may become more of a problem in larger areas as practices change or shift. Without effective insecticides for control of insect outbreaks, farms, communities, and entire regions of some states may suffer severe economic losses.
Biology and Life Cycle:
The seedcorn maggot is the larva of a small fly. The flies are attracted to fields where relatively fresh animal manure, green manure and other organic material are present. Seedcorn maggots seek out germinating soybean and corn seeds and eat the germ, killing the plant. Rescue treatments are not available for control of seedcorn maggot. Therefore, most treatments are made in anticipation of problems or replant situations.
Pest Distribution and Importance:
Overall, seedcorn maggots are considered a minor pest in corn production. This pest tends to be 'spotty' in an infested field. Growers may be controlling seedcorn maggot with soil insecticides applied for rootworm, wireworms, etc.
Chemical Controls:
Biology and Life Cycle:
These insects attack the germinating corn seed or feed on roots. Generally, infestations are patchy in fields and depending on species, damage may recur in succeeding years. Rescue treatments are not available for control of these pests, therefore most treatments are made in anticipation of problems or replant situations.
Pest Distribution and Importance:
These pests are of moderate importance to corn production, though they are becoming more prevalent. White grubs rank second to corn rootworm in NW Iowa. Wireworms are perceived by producers to be more of a problem west of the Missouri River whereas white grubs are more of a problem east of the Missouri River. Both could become more serious as cultural practices change. White grubs have historically been worse after sod and may be more of a problem where forages are included in rotation with corn (species dependent). White grubs tend to be more problematic in earlier planted corn and control is dependent on the number of grubs present. White grubs have a three year life cycle and are harder to control in the more mature stages (3rd yr) year. Annual white grubs rarely cause economic damage to corn
Chemical Controls:
Biology and Life Cycle:
Adults lay eggs in late summer and early fall which hatch in early June of the following year. Corn rootworm (CRW) larvae feed on a narrow range of host species. In general, a corn-soybean rotation disrupts their life cycle and constitutes the most effective management tool available for many farmers. Some populations of NCR have shown a life cycle adaptation called extended diapause. Extended diapause occurs when some of the eggs rest through the next summer and hatch the second spring after being laid. With extended diapause, control by a corn-soybean rotation can fail. This is currently occurring in parts of Minnesota, Iowa, South Dakota, Illinois, Indiana, (and to a lesser extent) Michigan and Ohio, and has resulted in a change in the dynamics of insecticide use in those areas. Recently, populations of WCR have lost a preference to lay eggs in corn, and prefer to lay eggs in other non-corn crop fields, such as soybean. This phenomenon occurs in northern (near the Wisconsin border) and east-central Illinois, northern Indiana, and northwestern Ohio. With WCR soil-applied insecticide treatments are generally a standard practice in corn acreage following corn and non-corn crops that target the larvae.
Pest Distribution and Importance:
This pest has significant importance to corn production. Rootworm transgenic hybrids may become available in near future, but are targeted to control only rootworms. As a result, they may not reduce the overall perceived risk of insect complexes and associated pesticide use. Rootworm insecticides are applied in furrow or in bands. Rootworms survive in the untreated areas, therefore allowing part of the field to remain untreated has relieved the resistance problems. Foliar broadcast applications targeted against adult rootworms have been used in the western Corn Belt in addition to in-furrow or band applications.
Chemical Treatments: (Soil-applied insecticides for larval control)
Chemical Treatments for Adult Beetles
In the eastern Corn Belt, in areas of continuous corn; growers are encouraged to rotate crops. In the western Corn Belt treatment for adult beetles primarily occurs to prevent economic egg laying.
Biology and Life Cycle:.
Corn borers overwinter as larvae in corn stalks and pupate in the spring. Moths emerge from these pupae in May and June, the adults mate and females place eggs on the underside of corn leaves and on other suitable plant species. A second generation occurs in late July-August. In the northern Corn Belt only one generation may occur (univoltine populations). The moths prefer the tallest corn for oviposition, and when larvae hatch, they feed on leaf tissue. These larvae mature and pupate, with a second emergence of moths, usually occurring in late July and August.
Second-generation ECB moths prefer late maturing corn for oviposition. The newly hatched second generation larvae feed lightly on leaves, but soon bore into leaf midribs, stalks and ear shanks.
Ear droppage is a problem and stalk tunneling can predispose plant to stalk rots. Economic thresholds for second generation corn borer are difficult to determine because of the long time period of egg laying an the relatively short persistence of foliar insecticides.
Pest Distribution and Importance:
This pest is of significant importance to corn production but is quite variable from year to year.
Bt products have helped with control but refuge areas need other pesticides for effective control. Insect resistance management plans are mandated by law. Bt corn adoption is 10-20% in most eastern Corn Belt states and is above 30% adoption in Minnesota. Adoption also depends on previous year insect populations. Comparing yield and quality losses due to insect pressure, corn borer potentially causes more economic damage than corn rootworm. However, growers seldom treat infestations because the spray window for each generation is short, multiple sprays are sometimes needed, and growers are unsure if the cost of chemicals will be returned. The pest is also difficult to scout - especially second generation. Where rescue treatments are utilized, the product formulation is critical for effective control. When rescue treatment timing is accurate, granular products can give better control of first generation than liquid forms. For rescue treatment of 2nd generation - liquid products provide better control than granular formulations. In the eastern region of the Corn Belt, Kentucky tends to see more Bt usage towards corn borers than other states, and most of that is directed at the southwestern corn borer (See section below). Some corn varieties have a natural tolerance to this insect. Areas where both univoltine and bivoltine corn borers occur presents a problem (i.e. continuous emergence of new adults provides no clear cut generations to target with insecticides.)
Chemical Treatments:
Biology and Life Cycle:.
Its life history and seasonal occurrence are similar to ECB. The second generation egg laying usually coincides with silking stage corn. Eggs are laid on both the upper and lower leaf surfaces.
Heavy second generation infestations can develop even in areas where first generation activity was light.
In addition to the types of damage caused by ECB, second generation SWCB larvae increases harvest losses through plant lodging caused by girdling of the stalk 1 to 2 inches above the soil. While the biology of SWCB is similar to that of ECB, peak moth flights occur after those of ECB, causing extended periods of corn borer larval activity. Weather-related planting delays can cause serious exposure to harvest losses by late-season SWCB.
Pest Distribution and Importance:
SWCB usually causes only light damage to early planted corn. In late corn plantings, first generation larvae can tunnel deep enough to kill the growing point and cause "dead heart". SWCB is not controlled by DIMBOA based plant resistance which protects small plants from ECB feeding. Treatment for second generation SWCB is generally applied when 20 to 25% of the plants are infested with eggs. Often a second application 7 to 10 days after the first is needed if significant egg laying occurs after the first application. In BT corn, the same hybrids that have good ECB resistance are also resistant to SWCB. When considering chemical control of second generation SWCB, consider presence of spider mites in making product selection. In the eastern and southern portion of the Corn Belt; parts of Illinois, Indiana, Kansas, Kentucky, and Missouri, there is a complex of ECB and southwestern corn borer (SWCB) attacking field corn. In these areas, economic losses attributed to SWCB is more frequent.
Chemical Controls
Biology and Life Cycle:.
A number of cutworm species cause stand losses to young corn in the first month of growth.
BCWs do not overwinter in the north central states. Southerly winds carry moths north from overwintering areas along the Gulf of Mexico, and mated females lay their eggs in fields. The moths prefer weedy areas and plant residue to lay eggs. Other cutworm species do overwinter in the Midwest, survival varies with winter weather.
Pest Distribution and Importance:
Prophylactic treatments are not recommended because of the sporadic nature of the infestation patterns and intensities. In northern regions, tillage or burn down herbicides applied at least two weeks before planting greatly reduces damage by this pest. Sporadic pest with catastroand the PHIc results when it occurs, occurs more frequently in the southern portion of the region, and should be considered a pest of significant importance. Biotech Bt corn for cutworm is available in some hybrids. Scouting is recommended and thresholds have been developed. After the V6 stage corn is tolerant.
ChemicalTtreatments:
Biology and Life Cycle:
Stalk borers are a native insect that damage corn by tunneling into plants and typically destroying the growing points. Damage is typically confined to field areas that are adjacent to borders of perennial grasses and broadleaf weeds, including road ditches, terrace backslopes, and grassed waterways. Perennial grasses like quackgrass and wirestem muhly and large broadleaf weeds, especially hemp (Cannabis sativa) and giant ragweed (Ambrosia trifida) are favored oviposition sites in the fall, and if these weeds are disseminated throughout the field, general damage can occur. Typically, stalk borer damage is limited to border rows, and treatments can be targeted to those border areas.
Pest Distribution and Importance:
This pest has a moderate level of importance; but local outbreaks can have a significant impact on yields.
Chemical Treatments:
Biology and Life Cycle:.
Corn leaf aphids are colonial sucking insects that can rapidly increase population numbers to cover the emerging tassels and youngest leaves of stage R1 corn plants. Although corn leaf aphids populations approaching 400 individuals per plant are necessary to warrant treatment, such populations do occasionally occur under favorable (dry) weather conditions. The primary damage from large populations is physiological, but secretion of honeydew can cause tassels to gum up and can reduce the effective dissemination of pollen. Scouting is most critical under drought conditions, and seed corn producers must pay special attention to protect pollen availability from inbred lines.
Pest Distribution and Importance:
Except under very dry conditions, this pest is of minor importance to corn production in most areas. This pest does not overwinter in most of the Corn Belt. Where there are heavy Johnsongrass infestations are controlled populations may move to nearby corn. Also carry the Maize Dwarf Mosaic (MDMV) virus.
Chemical Treatments:
Biology and Life Cycle:
Corn flea beetles are small insects that feed on corn leaf surfaces where they abrade the surface tissue and cause minor loss of leaf photosynthetic material. Flea beetles play a major role in the transmission of Stewart's wilt, a bacterial disease of corn. The incidence of Stewart's wilt is generally tied to winter conditions that favor winter survival of corn flea beetles. The average air temperatures (in degrees F) for December, January and February are added and if the total is greater than 95, Stewart's wilt is of special concern. If the 3-month sum of averages is below 95, the risk is relatively small.
Pest Distribution and Importance:
Scout and apply rescue treatments should corn flea beetle numbers reach the economic threshold. Treatment is seldom used unless the producer can justify a broad spectrum insecticide to control other existing insects. This pest is considered of minor importance to field corn in most areas of the eastern Corn Belt. More important to seed corn production because of inbred susceptibility to Stewart's wilt, and higher productive value.
Chemical Treatments:
Biology and Life Cycle:.
One generation per year occurs in the Midwest. Webworms that attack corn overwinter as partly grown caterpillars which developed in sod or other grasses the previous summer and fall. Larvae feed on leaves and may also cut the stalk like cutworms. Larvae are active as soon as corn emerges. Threshold levels for control are similar to corn cutworms.
Pest Distribution and Importance:
This insect is an occasional pest of corn and treatments are rarely required. This is a minor pest to corn production, usually in fields of corn planted into grass sod.
Chemical treatments:
Biology and Life Cycle:
Hop vine borers are soil dwelling and bore into the base of young corn plants where they destroy the growing points. Localized infestations can be intense and are often associated with weedy fields.
Pest Distribution and Importance:
Very targeted regionally - very similar life cycle to stalk borer - more of a pest in the northern latitudes. Considered a minor corn production pest. Timing of controls must be exact.
Chemical Treatments:
Biology and Life Cycle:.
Armyworm damage is characterized by ragged feeding and large amounts of frass (fecal pellets) on plants. The most severe damage occurs in corn fields that are no-tilled into grass or alfalfa sod. The grass is a favored oviposition site for adult moths that arrive from the gulf-coast states on strong southerly winds, similar to black cutworm. Often, the damage to young corn happens suddenly when the grass supply is consumed or when it is killed with a herbicide treatment. No-till fields must be observed closely, and treatments should be based on the presence of small army worm larvae feeding on the grass and the level of damage to corn.
Pest Distribution and Importance:
Very sporadic, but when it appears, it can be a significant pest - capable of destroying entire fields. Armyworms often move from wheat fields to corn fields as the season progresses. Scouting and spraying of field perimeter is an effective method of control - no-till corn field near rye or other grassy field. Bt corn is effective in controlling armyworm infestations. This pest is considered of low to moderate importance to corn production.
Chemical Treatments:
Biology and Life Cycle:
Twospotted spider mite has very broad host range, reproducing on grass and broadleaf crops and weeds. Banks grass mite is restricted to grassy crops and weeds. Both species have high reproductive rates, and short life cycle and can produce multiple generations in a growing season. Spider mites feed on the underside of lower leaves, moving up the plant as populations develop. They feed by sucking juices from leaf cells, leaving yellow dots where they feed. When abundant they can kill leaves. Infestations at the level of the ear often cause economic yield losses.
Populations may increase after insecticide applications made for other insects, because broad spectrum
insecticides kill predatory insects and mites which help suppress mite population growth. Populations
may rebound quickly after miticide application, because except for propargite, miticides are not effective
against eggs, and miticides also kill mite natural enemies (predatory mites and insects).
Pest Distribution and Importance:
Spider mites are controlled during most years by a naturally occurring disease and arthropod natural enemies (predator spider mites and insects). However, when there are prolonged periods of low humidity, the fungus is suppressed, allowing the spider mite population to proliferate. If adverse weather conditions continue, re-treatment may be needed. In the eastern Corn Belt region it is not considered a pest of importance on corn. More commonly they are a pest in the western Corn Belt. Two spotted spider mites are less susceptible to most pesticides than Banks grass mite. Banks grass mite may colonize corn early in the season as small grains or pasture grasses mature. Two spotted spider mites normally colonize corn later in the season (late whorl-reproductive stages)
Chemical Controls:
Spot treatments are recommended if only part of the field is infested; re-infestation and resurgence is possible after treatment due to egg hatch and destruction of beneficial insects and mites.
Biology and Life Cycle:.
Grasshoppers are common mid- to late-summer pests of corn. These insects hatch in grassy field edges and other grassy areas where they will feed, and then gradually spread into production fields. The presence of grasshoppers in border areas is not necessarily a cause of alarm. Adult grasshoppers are better controlled with some of the pyrethroid and carbamate insecticides.
Pest Distribution and Importance:
Cultural practice of delayed mowing of ditch banks etc will assist in keeping the grasshoppers out of production fields. Grasshoppers are considered of low importance to corn production. Greatest yield losses are caused by the loss of leaf area during tassel and silking stages. A 20% loss of leaf area during this time will result in about 7% loss in yield. However, scouting is pertinent, because it is important to only treat when the population reaches economic thresholds.
Chemical Treatments:
Biology and Life Cycle:.
Western bean cutworm is a pest that can severely damage ears, resulting in potentially large yield and grain quality problems. One generation per year; larvae overwinter in soil. Populations survive overwintering best in well drained soils. The adults oviposit on upper surfaces of corn leaves or on dry edible field bean leaves. Corn fields in late whorl stage are the most attractive to females for egg laying. New larvae are about ¼ inch in length and are dark brown. These larvae feed on pollen and then move to ears where they feed until dropping to the ground and form a subterranean overwintering chamber.
Pest Distribution and Importance:
Timing of treatments is critical, because once the larvae reach the ear tips they are then shielded from the insecticide. Fields treated with pyrethroid insecticides should be monitored closely for subsequent spider mite infestations. University of Nebraska recommendations are to scout with the beginning of moth flight in the middle of July. The economic threshold is reached when 8% of the plants have eggs or larvae in the tassel. Typically a pest in Nebraska, Kansas, Colorado; recently has also been found in NW Iowa and southern MN.
Chemical Controls:
Pesticide classes for the insecticides listed above are indicated in the following table. The table also presents intervals required for Restricted Entry (REI) and for preharvest intervals (PHI).
Table 2. Insecticides, Trade Names, REI and And the PHI, and the Estimated Percent of Acres Treated Annually.
| Chemical | Trade Names | Restricted Entry Interval | Preharvest Interval | Percent acres treated |
| Insecticides and Miticides | ||||
| Bacillus thuringiensis | Dipel, MVP, Javelin | 4 hrs | 0 d | |
| Bifenthrin | Capture | 24hrs | 30d | 2 |
| Carbaryl | Sevin | 12 hrs | 1 d | |
| Carbofuran | Furadan | 2-14d | 30 d | |
| Chlorethoxyfos + Cyfluthrin | Fortress | 48-72hrs | ||
| Chlorpyrifos | Lorsban | 24 hrs | 4E 35d 50W 28 d |
6 |
| Cyfluthrin | Baythroid | 48hr or 72hrs if rain<25in/yr | NA | |
| Diazinon+Lindane | Kernal Guard | NA | NA | |
| Dimethoate | Cygon | 48 hrs | 14 | |
| Esfenvalerate | Asana | 12 hrs | 21 d | |
| Fipronil | Regent | 24hrs | 90d | 4 |
| Imidacloprid | Gaucho, Prescribe | 12 hrs | 7 d | |
| Lambda-cyhalothrin | Warrior 1 EC | 24hrs | 21d | |
| Methyl Parathion | Penncap-M | 48 hrs | 2-4pts 14 d >4pts 21 d |
|
| Methomyl | Lannate | 48hrs | 21d | |
| Permethrin | Ambush, Pounce, Kernel Guard Supreme | 12 hrs | 30d | |
| Phorate | Thimet | 48hr or 72hrs if ran<25in/yr | 30d | |
| Propargite | Comite | 7d | 30d | |
| Spinosad | Tracer | 4hrs | 28d | |
| Tebupirimphos | Aztec | 48 hrs | NA | |
| Tefluthrin | Force, Force ST, Proshield (seed trtmts) | 0hrs | NA | |
| Terbufos | Counter | 48 hr or up to 72 hr where ave rain < 25 in/yr | NA | |
Biology and Life Cycle:
As indicated for each pest in the text below.
Pest Distribution and Importance:
Granary Weevil (Sitoand the PHIlus granarius L).
This weevil, along with the closely related rice weevil, is among the most destructive of all stored grain insects. The larvae develop inside kernels of whole grain in storage, thus making an infestation difficult to remove in the milling process. In Indiana, the granary weevil is largely a pest of stored wheat, corn, and barley, especially in elevators, mills, and bulk storage. The adult cannot fly, and field infestations do not occur.
Saw-Toothed Grain Beetle (Oryzaeand the PHIlus surinamensis L).
Along with flour beetles, the saw-toothed grain beetle is one of the most common insects in stored grain and cereal products. The larvae develop in flour, cereal products, and many other dried foods. For this reason, it is a common pest not only in grain bins, but also in elevators, mills, processing plants, warehouses, and kitchens. In grain bins, it feeds on broken kernels and grain residues.
Red Flour Beetle (Tribolium castaneum [Herbst]).
This beetle is similar to the saw-toothed grain beetle in habits and types of products infested. It is a serious pest in flour mills and wherever cereal products and other dried foods are processed or stored. Like the confused flour beetle (not pictured), the red flour beetle may impart a bad odor that affects the taste of infested products.
Larger Cabinet Beetle (Trogoderma inclusum [LeConte]).
Representing a group also referred to as Trogoderma, the larger cabinet beetle is a scavenger that feeds on cereal products and dried animal matter. The fuzzy, slow-moving larvae -- similar to the larvae of carpet, hide, and larder beetles -- often are found crawling about on or near the products they infest.
Lessor Grain Borer (Rhyzopertha dominica [Fabricius]).
This pest is most common and destructive in warm climates but can spread to any area in transported grain. It is a problem of grain only and not cereal products. The larvae develop inside the kernels of whole grain. The adults also damage grain by boring into the kernels and leaving them covered with powder from the chewed material.
Rice Weevil (Sitoand the PHIlus oryzae L).
The rice weevil is similar to the granary weevil in both appearance and habits. The name is misleading, however, because it infests other grains besides rice. Adults can fly and, in warm climates, can cause widespread damage to corn, wheat, and other grains before harvest. Although field infestations do not occur in Indiana, post-harvest infestations do. Such infestations originate from shipped-in grain or from already infested storage.
Indian Meal Moth (Plodia interpunctella [Hübner])
Common to both stored grain and cereal products, Indian meal moth larvae cause damage in corn meal, packaged foods, bagged grain, and grain in storage. Attack is confined to surface layers of stored shelled corn and small grains. In the case of stored ear corn, however, feeding occurs anywhere because the moths crawl among the ears to lay their eggs. Larval feeding is characterized by a webbing of the material infested. The mature larvae then often leave the material and crawl about in search of a place to pupate.
Cadelle (Tenebroides mauritanicus L).
Both the adult and larvae are large and easy to see. Both stages feed mainly on the germ of stored grains, but may also attack milled cereal products. The larvae leave stored grain in the fall and burrow into woodwork, such as wooden bins or boxcars, to hibernate. They may also burrow into packaged cereal products, thus providing an entrance for other cereal pests.
Flat Grain Beetle (Cryptolestes pusillus [Schönherr]).
This is a tiny beetle that feeds primarily on the germ of stored grains, especially wheat. It is readily attracted to high-moisture grain. In fact, under high-moisture conditions, the flat grain beetle may also develop in many cereal products, but is not a common pest in kitchens.
Angoumois Grain Moth Sitotroga cerealella [Olivier]).
This is a common and destructive pest of crib ear corn. It also infests stored shelled corn, and other small grains, but attack is confined to the surface layer of grain. Field infestations are common in the southern half of Indiana. The larvae develop within the kernels; therefore, the Angoumois grain moth is not a pest of cereal products. Infestations in homes often occur in stored popcorn or in colored ears of corn kept for decoration purposes. The moth resembles the clothes moth but does not shun light.
Chemical Treatments:- None indicated
Other Pest Management Aids:- None indicated
Diseases are present to some extent every year and are responsible for reductions in both yield and grain quality. Losses from diseases vary from year to year and their occurrence is strongly influenced by weather conditions. While some diseases occur commonly they may not cause much damage, yet others have the potential to be very serious.
Throughout most corn producing states, farmers are utilizing conservation tillage systems that assist in soil and water retention. The presence of a mulch layer from previous crops modifies many of the physical, chemical, and biological components of the soil and its ecosystem. Numerous studies have documented changes in temperature, water retention capacity, soil microbiology, soil tilth and structure, and chemical composition when farmers have modified their tillage from conventional tillage to either reduced or no-tillage systems. These micro-environmental changes can have a significant impact on crop diseases.
Conservation tillage practices result in a continuing emphasis on seed treatments for corn establishment. Also, a trend toward early planting exacerbates disease producing conditions in both conventional and conservation tillage. Although improved crop vigor and better planting methods will aid in crop establishment, there will be a continued reliance on inexpensive seed treatments for effective disease suppression.
Population dynamics of root pathogens associated with crop residues may change dramatically as tillage systems change. Fusarium species of fungi, in particular, increase when residues are present. These fungi are common root rotters and also invade corn stalks, causing stalk rots. Higher disease incidence has also been reported with another common soilborne fungus, Rhizoctonia solani. This fungus infects virtually all common field crops and can reduce early season vigor and growth.
A third group of fungi that thrive in cool, wet soils are Pythium species. These fungi infect the mesocotyl region of corn (the mesocotyl tissue links the new plant with the primary root system). Mesocotyl infections, causing loss of the primary root system, result in reduced growth or death of the seedling. The cooler and wetter conditions associated with reduced tillage increase activity of Pythium fungi.
Methods of controlling plant diseases in field corn characteristically fall into three categories. First, plant breeding efforts are the primary focus of improving plant resistance and tolerance to the chronic effects of plant disease wherever possible. Second, tillage and crop management options are utilized to minimize the impact of the disease. Third, the use of fungicides, both as seed treatments and as foliar applications, are used where necessary to prevent crop losses where breeding and cultural management techniques fall short.
Historically, plant breeding and crop management techniques have minimized the impact of many existing diseases. It is possible, however, that a new disease, new race, or a new biotype of an existing disease will negate much of the impact of plant breeding and crop management. It is for this reason that new fungicides and disease management techniques continue to be developed and available for use.
A key factor in the management of most corn diseases as indicated by producers throughout the Corn Belt is breeding so that organism-specific resistance and tolerance are maintained and improved. Field corn is a relatively low value crop on an acre-by-acre basis, and by the time that a corn disease breaks out significantly, there are either no effective rescue treatments, or the disease has progressed to the point that rescue treatments are not economically practical.
The group at the workshop representing the western Corn Belt, noted that breeding for drought resistance may be as important as breeding for crop disease resistance. These are not mutually exclusive efforts. Part of yield suppression from drought-stressed corn comes from the plants being predisposed to infection by pathogens that add to yield losses directly caused by the moisture deficit, and vice versa.
While it is generally accepted that the focus on high yields in corn breeding has resulted in corn plants with greater overall disease tolerance, grower observations suggest that some of the newest hybrids may have greater susceptibility to plant diseases. It is unclear at this time how plant populations, crop rotations, and other management practices may be contributory factors. If these observations prove to be true, there may be a greater need for foliar fungicide treatments in the foreseeable future.
Not all diseases are economical to treat. The use or non-use of a fungicide is highly dependent on the economics of corn production, the perceived losses caused by the disease, and the cost of the treatment. Many foliar diseases, once evident in the field, are difficult or impossible to treat effectively. As a result, field corn is seldom treated with foliar sprays. Seed decay and seedling blights, however, are almost always treated for with fungicidal seed treatments. Seed treatments are highly effective against these diseases and are very economical to use.
Though a number of fungicidal products and classes are available for plant diseases in field corn, it is deemed essential that this wide selection of products continue to be available to producers to provide the tools necessary for resistance management programs. As new diseases become evident and as existing diseases adapt to current cultural and chemical controls, it is important to have on hand effective and economical treatments. Though most diseases are sporadic in their occurrence and level of importance, without effective fungicides they can cause devastating losses for individual producers.
Throughout the discussion below comments are made regarding the relative susceptibility of sweet corn, popcorn, or other specialty corn types to field corn diseases. This information is provided because these corn types are relatively prevalent throughout the Corn Belt and they may be a source of inoculum for field corn diseases. Though seed corn is not covered specifically in this document, seed corn lines can be assumed to be more susceptible to all plant diseases listed below. It can therefore also be assumed that more seed corn is treated for diseases than is field corn.
Within the discussion of plant diseases below can be found a number of references to increased disease severity where the soils are cool, damp, and covered with residue. Almost without exception, fields that are poorly drained, planted early in the season, or managed with reduced till, have a higher incidence of plant diseases. Though each of these factors can be controlled by the grower in some degree, it is the latter factor, reduced tillage, that presents a dilemma for many growers as they try to reduce erosion and raise a healthy crop. For these growers, having effective fungicides for disease control remains a very high priority.
For discussion purposes, plant diseases are grouped below into broad categories. These categories include: Seed Decay and Seedling Blights, Root Rots, Foliar and above ground diseases, Ear and Kernel Rots, and Nematodes.
Biology and Life Cycle:
These diseases are generally caused by soil-inhabiting fungi such as Pythium, Fusarium, Diplodia, Rhizoctonia, and Penicillium. These fungi also may be seedborne, except for Pythium. Seeds may be rotted before germination or the seed may germinate and the seedling infected and blighted (damping-off). This can occur as either pre-emergence damping-off or post-emergence damping-off.
Pest Distribution and Importance:
Damping-off is favored by cool, wet soils, so it is more common in low-lying or poorly drained areas or in fields planted too early in the spring. Heavy residue on the soil surface can favor damping-off by suppressing soil temperature and drying. Other factors that delay germination and emergence such as herbicide damage, compaction, crusting, or planting too deep, can result in more seedling blight.
Seed/seedling diseases are controlled by seed treatment only. Human exposure, once the seed is in the ground, is minimal and would only occur when loading seed into planter and checking planter boxes or moving seed. Seed comes already treated in bag. Very little corn replanted due to seedling blight because of treated seed. Seed treatment lasts just long enough to get seed germinated. In the absence of seed treatments severe losses would be incurred in localized areas.
Chemical Controls:
Biology and Life Cycle:
Root rots of corn are very common, and can be caused by a number of fungal pathogens including Pythium spp., Fusarium graminearum and other Fusarium species, and Exserohilum pedicellatum. Root rots occur to some extent in every field.
Pest Distribution and Importance:
Wet soil conditions predispose plants to root rots because of oxygen deficiency, and the root rot fungi thrive under these conditions. Highly compacted or otherwise poorly drained soils are particularly prone to root rots. Many of the stalk rot pathogens enter through the roots and cause a root rot in advance of the stalk rot. Root rots are generally not economically significant and are considered of minor importance to corn production. But under wet conditions, root rots cause economic losses. Root rots are primarily controlled by resistant varieties. Root rots are not well understood by growers. No products are sold to control root rots, therefore very little research has been done on them. Root rots may be mis-diagnosed as another disease/injury. Excessive crop nutrients may affect amount of disease.
Chemical Controls:- The seed treatments used for seedling rots and seed decay have some limited effect on root rots. No products are specifically available and labeled to control root rots.
Other Pest Management Aids:
Biology and Life Cycle:
Eyespot is caused by the fungus Aureobasidium zeae, previously known as Kabatiella zeae. This fungus overwinters in corn residue and in wet conditions produces conidia that are spread by splashing water and wind. The disease is much more common when corn follows corn. Eyespot may appear early in the season on lower leaves and again near the end of the season on upper leaves.
Pest Distribution and Importance:
Eyespot is more prevalent in the northern part of the Corn Belt. Early maturing hybrids seem to be more susceptible. Field corn is seldom treated with foliar fungicides for this disease.
Chemical Controls
Biology and Life Cycle:
Common smut is caused by the fungus Ustilago zeae, previously known as Ustilago maydis, which overwinters in corn residue or soil. This fungus produces black teliospores that survive well in soil. These teliospores germinate during the spring and summer, with each teliospore then producing four smaller spores, called sporidia. Sporidia are spread by wind and water. All above ground plant parts are susceptible, especially the actively growing meristematic tissue. Sporidia can infect through unwounded cells, but wounds caused by insects, detasseling, cultivation, hail, or blowing soil are important infection sites as well.
Pest Distribution and Importance:
Disease is favored by excess nitrogen, excess manure or herbicide injury, and relatively dry, warm weather. This disease is of low importance to corn production. Smut is not a health issue to livestock when it contaminates feed.
Chemical Controls: - This disease does not receive chemical treatment.
Other Pest Management Aids:
Biology and Life Cycle:.
Northern leaf blight is caused by the fungus Exserohilum turcicum, previously called Helminthosporium turcicum. There are at least seven races of the fungus. The fungus overwinters as mycelium and spores in corn residue. Spores are dispersed by wind and splashing water.
Pest Distribution and Importance:
This has traditionally been the most consistently damaging leaf disease of field corn in the northern Corn Belt, but its severity has decreased due to improvements in resistance. It occurs throughout the eastern half of the United States, as far west as eastern Nebraska. Disease development is favored by extended periods of leaf wetness (rain or dew) and moderate temperatures (64-81°F). This disease is important to corn production but rarely treated.
Chemical Controls:
Biology and Life Cycle:.
Northern corn leaf spot is caused by the fungus Bipolaris zeicola, previously known as Cochiobolis carbonum. There are five known races of this fungus with different virulence characteristics and symptoms. Race 0 is nearly avirulent to corn, and race 1 is virulent on only a few genotypes. Races 2 and 3 are the most common races in the Midwest. Race 2 is not specific for corn genotypes, while race 3 is only a problem on certain susceptible lines. A fifth race has been reported recently. B. zeicola overwinters as mycelium and spores in corn residue, and the spores are dispersed by wind and splashing water.
Pest Distribution and Importance:
This disease is favored by high humidity and moderate temperatures. This disease rarely occurs in modern hybrids and is not treated with fungicides.
Chemical Controls:
Biology and Life Cycle:.
Anthracnose leaf blight is caused by the fungus Colletotrichum graminicola, the same fungus that causes anthracnose stalk rot. It overwinters as mycelium or sclerotia in corn residue or seed. Several weed species also are hosts and may act as inoculum sources. Spores are spread primarily by splashing water.
Pest Distribution and Importance:
Disease development is favored by wet weather with warm temperatures. Anthracnose is much more common where corn follows corn. Anthracnose is usually more severe in the eastern corn states, but its importance in the Midwestern states is increasing. This disease occurred in outbreak proportions in 2000, but was not much of a problem in 2001. Problems are usually localized but can be severe. There is a noticeable trends for greater occurrence in recent years. Anthracnose is not economical to treat for; normally too late to treat once symptoms are seen.
Chemical Controls:
Biology and Life Cycle:.
Gray leaf spot is caused by the fungus Cercospora zeae-maydis. The fungus survives as mycelium in corn residue, and spores are dispersed by wind and splashing water.
Pest Distribution and Importance:
This disease is a problem in the eastern United States, and it has grown in importance in the western Corn Belt as far west as central Nebraska. Gray leaf spot is much more common in the southern half of the North Central Region. It is particularly severe when corn follows corn and in areas of irrigation. In Michigan it is found predominantly where irrigation is used. Sporulation and disease development are favored by warm, humid weather.This is a widespread and economically significant problem in corn production. Some varieties have tolerance. The number one or two rated disease across the Corn Belt. By the time symptoms are readily apparent it may be too late for control measures.
Chemical Controls:
Biology and Life Cycle:.
This disease, also called Stewart's wilt or bacterial wilt, is caused by the bacterium Erwinia stewartii, which overwinters in the gut of the corn flea beetle (Chaetocnema pulicaria). The occurrence of this disease is strongly linked to the winter survival rate of the corn flea beetle, because the beetle introduces the pathogen into the corn plants as it feeds and carries the bacterium from plant to plant. The beetles survive in high numbers following a mild winter, resulting in high disease levels. If the sum of the mean monthly temperatures for December, January and February is 90°F or more, the beetles will survive and the threat of Stewart's wilt is high. The disease can be spread by insects other than the flea beetle, but they are not as important. Stewart's disease is also seedborne, but seed transmission is very rare.
Pest Distribution and Importance:
This disease is more common in the southern and eastern parts of the Corn Belt. Dent corn is not very susceptible except for a few inbreds, but sweet corn can be very susceptible. This disease is of increasing importance in recent years. Perhaps because more flea beetles are able to overwinter due to mild winter temperatures. Monitoring for flea beetles is important. Winter annual weed control can reduce concerns with beetles. This disease is considered of low to moderate importance to field corn production but economical losses are possible if severe (insect) problem is not treated. This disease has a lower economic threshold than other diseases. Therefore, scouting for flea beetle after corn emergence is very important. Stewart's wilt can be managed to a great degree with hybrid selection.
Chemical Controls:- Control flea beetles, no cost effective treatments for disease. See the insect section of this report for products that control flea beetles as they also control Stewart's wilt.
Other Pest Management Aids:
Biology and Life Cycle:.
Stalk rots are a consistent problem in corn production, causing yield losses through premature plant death and/or lodging. When plants die prematurely, the result is poor yields and low test weight grain. If a plant with severe stalk rot survives to maturity, yield may not be greatly affected. However, rotted stalks will easily lodge, making harvest impossible. Stalk rots are caused by several different fungi that infect plants through the roots or through wounds in the stalk. The major stalk rot pathogens are Gibberella zeae, Fusarium species, and Colletotrichum graminicola (anthracnose), and Diplodia sp.
Pest Distribution and Importance:
The occurrence of stalk rots is strongly affected by stresses on the corn plant during the grain filling stage of development. Any conditions that reduce photosynthesis and the production of sugars can predispose the plant to severe stalk rot. Such stresses include high plant populations, severe leaf diseases or hail damage, drought or soil saturation, lack of sunlight, extended cool weather, low potassium in relation to nitrogen, and insect damage. Insects such as the European corn borer cause stress to the plant as well as providing wounds for entrance of the stalk rot fungi. Many stalk rot infections can be traced back to stalk boring insect wounds. Early maturing hybrids sometimes suffer more stalk rot damage than full-season hybrids. Stalk rots are a sporadic and seasonal problem and are generally considered of minor importance in corn production.
Chemical Controls:- None indicated.
Other Pest Management Aids:.
Biology and Life Cycle:
Fusarium Rots
Fusarium ear and kernel rot is the most common ear disease in the Midwest. It is caused by several fungi in the genus Fusarium, but F. moniliforme is considered to be the primary species on corn in the Midwest. Fusarium ear rot occurs under a wide range of weather conditions. The fungus causes a stalk rot and can colonize any part of the corn plant, overwintering in the corn residue and on dead grassy weeds. F. moniliforme also is commonly found in corn seed. Fusarium spores are spread by wind and splashing rain to the silks, which are most susceptible for the first 5 days after they appear. Infections also occur through wounds made by insects or other types of wounds in the kernels. There is some evidence that insects act as vectors of Fusarium. F. moniliforme can grow throughout the corn plant, and some ear infections may be the result of the fungus entering the ear through the shank. Several of the Fusarium species causing corn ear rot can produce harmful mycotoxins, so caution should be used in feeding molded corn. Fusarium species usually do their damage in the field, but they can be a problem in storage if grain moisture is 18 percent or above.
Gibberella Ear Rot
This ear rot is common throughout the Midwest. It is caused by the fungus Gibberella zeae which is the sexual reproductive stage of Fusarium graminearum. This fungus also causes a stalk rot, and overwinters in corn residue. The spores are spread by splashing rain and wind infecting ears through the silks. Silks are most susceptible 2 to 6 days after emergence. The disease is favored by cool, wet weather after silking. This is the most consistently important mycotoxigenic fungus in the northern Corn Belt, producing vomitoxin, zearalenone, and other toxins. Fusarium species usually do their damage in the field, but they can be a problem in storage if grain moisture is 18 percent or above.
Diplodia Ear Rot
Diplodia ear rot is caused by the fungus Diplodia maydis (Stenocarpella maydis), which also causes Diplodia stalk rot. This disease is not typically as common as Fusarium or Gibberella ear rots, but it can be destructive when it occurs. The fungus overwinters as mycelium, spores, and pycnidia on corn residue or seed. The spores are spread primarily by splashing rain. The infection process for this disease is poorly understood, but infections first appear at the base of the ear. Corn borer damage in the shank can provide an entry wound for the pathogen. Diplodia rot is favored by cool, wet weather during grain fill. Rainfall during August, September, and October is correlated with Diplodia ear rot incidence. D. maydis is not known to produce harmful mycotoxins. Diplodia maydis usually does its damage in the field, but it can be a problem in storage if grain moisture is 20 percent or above.
Aspergillus
Aflatoxin is the main grain mycotoxin of concern.
Pest Distribution and Importance:
Control of the various ear and kernels rots can be achieved by similar practices. Prevention of their occurrence is difficult because of their dependence on weather and the limited affects of cultural practices. Control of these diseases places an emphasis on harvest and grain handling. These diseases have a high importance to corn production as the toxins produced by molds can be a serious health issue for humans and livestock. Diplodia is known to be more severe in some specialty corn types such as high oil corn. Concern over these diseases could rapidly escalate if FDA sets levels for mycotoxins at unachievable levels.
Chemical Controls:- None indicated.
Other Pest Management Aids:
Plant more tolerant hybrids. Tolerance to the ear rots varies among hybrids, although complete resistance is not available. Hybrids with tight husk coverage and ears that do not remain erect after maturity tend to suffer less damage. (Keep moisture out of ear).
Crop rotation can reduce the occurrence of some ear rots, such as Diplodia. Others may not be affected much because of the movement of spores from neighboring fields.
Control of insect and wildlife feeding may reduce ear rots to some extent. Scout fields as the corn begins to dent and identify areas with mold problems. Harvest these areas as soon as possible to prevent further mold development.
Properly adjusted combines will reduce kernel damage. Damaged kernels are more susceptible to mold development. Combine adjustments also can be used to help discard light weight, moldy kernels during combining. Cleaning grain before drying will remove the fine particles that are often the moldiest and most toxic component of grain.
Moldy grain should be dried immediately and rapidly to 15 percent or less (13-14 percent for long-term storage). Holding this grain for even a short time can result in substantial mold and toxin development. Grain that does not have obvious mold problems also should be dried immediately, but there may be more economical options to rapid, high-temperature drying. Cool the grain after drying.
Clean bins before storing new grain. Aerate and stir stored grain; periodically check for condensation and mold growth. Control storage insects.
Antifungal agents such as propionic acid can retard mold growth in storage, but they do not kill fungi already present or destroy toxins that are already formed. These compounds have some disadvantages.
Test molded grain for mycotoxins prior to feeding. Dry and market corn immediately. Don't store it.
Table 3. Fungicides, Brand Names, REI and And the PHIs, and the Estimated Percent of Seed or Crop* Treated Annually
Chemical |
Brand Names |
Restricted Entry Interval (hrs) |
Preharvest Interval Days | Percent Acres Treated |
Fungicides and Bactericides |
Applies to foliar applications only | Applies to foliar applications only | Blanks indicate amounts between 0 and 1 percent | |
| azoxystrobin | Quadris | 4 | 0 | |
| captan | Captan | 96, 48 w/prot. equip. | 0 | 20 |
| chlorothalonil | Bravo | 48 | 14 | 1* |
| fludioxynil | Maxim | (NA) | NA | 80 |
| mancozeb | Dithane Mancozeb | 24 | 77 Ext. program | 1* |
| metalaxyl | Apron | (NA) | NA | 99 |
| meefenoxam | Apron XL | 48 | NA | ? |
| propiconazole | Tilt | 24 | 0 | 2* |
Biology and Life Cycle:
Nematodes that attack corn are microscopic roundworms, approximately 3/10 to 3/64 inch long. There are many species of nematodes that feed on corn. Dagger and spiral nematodes may be the most common and widespread nematodes
Pest Distribution and Importance:
Every cornfield contains nematodes actively feeding on plants. The presence of nematodes depends on the soil type and its properties, other soil microorganisms, cropping history, climatic factors such as temperature and rainfall, tillage practices, and the use of pesticides. Corn nematodes can feed without causing appreciable yield loss if nematode numbers are low and/or the environmental conditions are such that the corn crop is not stressed. Needle nematode probably is the most damaging, but is not widespread. The most important species that is a parasite on corn is the lesion nematode.
Nematicides:
Many effective nematicides have been removed from the market and very few new nematicides are being developed, but a few compounds (including some soil insecticides) are still labeled for control of plant-parasitic nematodes on field corn.
Other Pest Management Aids:.
Management options for control of nematodes on corn are limited. Cultural control strategies such as crop rotation, delayed planting, and alternative tillage have little effect on corn nematode densities and nematode-resistant corn hybrids are lacking.
A ban on atrazine would result in increased costs for alternative products notwithstanding any considerations of lower yields due to reduced weed control. Initial cost estimates may be overly conservative if the fact that atrazine exerts a suppressive effect on the market price of other corn herbicides is not considered. Weed management programs that are based on crop scouting, sequential herbicide applications, and maximum use rates of 1 lb a.i. atrazine per acre would also increase in cost compared with conventional soil-applied, one-pass herbicide applications that contain 1.2 to 2.0 lbs atrazine a.i. per acre. To such costs can be added an additional $3 to $7 per acre for crop scouting and additional trips across the field may cost $4 to $6 per acre sans herbicide.
Though overall cost remains a major constraint to widespread planting of glyphosate and glufosinate tolerant hybrids, the cost of glyphosate has declined significantly. In the northern corn belt (e.g. the Dakotas), where fewer atrazine options are available, the Roundup Ready hybrids have been adopted more quickly than in other areas of the corn belt.
Resistance management and weed shifts are major concerns in areas where glyphosate-resistant soybean are planted on a large percentage of the production acres. Continuous planting of both glyphosate-tolerant corn and soybean invites weed resistance or ecological shifts to more tolerant weed species. Key weed pests have already developed enhanced tolerance to glyphosate in select areas of the Corn Belt, and winter annuals are becoming an increasing problem affecting early spring corn planting because glyphosate has supplanted use of residual herbicides in soybean production which previously suppressed winter annual germination and establishment in the fall.
The infrastructure to handle a predominantly "post-emergent" weed control system in corn may not exist throughout the Corn Belt. The Spring of 2002 was an example of a year where the application window on corn was relatively narrow, and on many days it is either too windy to spray or fields are too wet to support spray equipment. Strict reliance on post-emergence herbicides would have resulted in many fields going untreated.
Wind and drift are important issues if regulatory actions impose a greater emphasis on post-emergence herbicide application. If producers depend too much upon post-emergence herbicide programs and EPA puts more emphasis on drift control, then making timely post applications becomes even more problematic for corn producers.
Atrazine "alternatives" such as mesotrione (Callisto) and isoxaflutol (Balance) have achieved fair to good results with higher rates applied pre-emergence. However, the pricing structure present today makes preemergence applications of these products an unlikely choice for many producers. Rates of these new products can be significantly reduced when tank-mixed with low rates of atrazine (i.e. < 1 lb a.i.) making these applications more cost affordable.
Research throughout the Midwest has shown that groundwater contamination from atrazine can be a problem in areas where soil conditions allow rapid transport to shallow groundwater. These localized areas, however, represent a minute fraction of corn production acres. (Midwest Studies Provide Some Answers, 1999 MSEA Regional Publication)
Research shows that attaining 90% control of all weeds in no-till systems occurs less frequently than in conventional-till systems. Two-pass programs provide 90% or higher control more often than one-pass programs regardless of tillage system. The addition of atrazine increases the frequency of attaining 90% control. However, one-pass programs do not provide 90% control when atrazine is not used, regardless of tillage system. (University of Missouri, 10-year study, B. Johnson et. al.)
Atrazine levels in surface water runoff may be problematic in areas of the Corn Belt characterized by the combination of high rainfall in April and May, land use patterns (e.g. >15% of county acres planted to corn), and soils with moderately high to high runoff potential (i.e. high clay content subsoils with argillic horizons). These areas encompass Major Land Resource Areas 109, 112, 113, and 114. (Atrazine Management and Water Quality, M. Smith et al., Missouri Manual 167) Though research and on-farm demonstrations have shown that atrazine levels in surface water reservoirs can be reduced up to 74% through adoption of weed management programs that utilize crop scouting and sequential herbicide applications, these techniques are not universally adopted.
In 1997 weed specialists from the major corn producing states were interviewed with regards to losses due to weeds in corn. Their estimates of losses totaled 1.25 billion dollars annually or about $16 per acre. This loss included reductions in yield and quality but did not include costs of control. Losses would have been 30 to 50 percent greater if estimates from all specialists in corn producing states had been included and if all weeds were considered. Typically herbicide expenses range from $15 to $25 dollars per acre and tillage and other mechanical weed control expenses can conservatively average $5 to $15 per acre annually. Combining estimates suggests that costs will average more than $45 dollars per acre for weed control and losses due to weeds.
Weeds reduce corn yield primarily by competing for water, sunlight and nutrients, thus diminishing total corn yield potential. Heavy weed infestations can also affect harvest efficiency by increasing grain moisture content at harvest and increasing foreign material levels in harvested grain, both resulting in added cost to the producer. Weeds can also harbor or host insect and plant diseases.
Within this document weeds are grouped in logical categories for discussion purposes. Annual species comprise the majority of the weeds found in corn production. Many of the primary weed species are introduced rather than native. Native and non-native plants become weeds because they are adapted to the two-crop rotation system primarily used throughout the Midwest, germinate at or near the same time as the crop, and are able to produce seed before the crop is removed by harvest.
Increases in conservation tillage practices have resulted in a greater prevalence of weeds from three different classes; perennial weeds (ex. common milkweed, hemp dogbane, and bigroot morningglory, etc), small seeded grass and broadleaf weeds that produce seeds able to germinate near the soil surface (ex. fall panicum, lambsquarters, pigweeds, etc), and winter annual weeds (ex. common chickweed, henbit, and numerous mustards).
In addition, weed species that have developed resistance to herbicides have in many cases become more prevalent (ex. shattercane, giant foxtail, cocklebur, kochia, and lambsquarters). The most significant resistant weeds in recent years are the tall and common waterhemp species.
Information on the level of control of weeds for listed herbicides is not given in this section but is presented in an aggregate table at the end of this document. For up-to-date information on herbicide rates and acres treated please see http://usda.mannlib.cornell.edu/reports/nassr/other/pcu-bb/#field
Biology and Life Cycle:
Grass weeds germinate at soil depths from 1/8th of an inch to 2 or 3 inches. Seed size and dormancy are the controlling factors for when and where these seeds emerge. Large seeded weeds have greater seed food reserves and can emerge from greater soil depths where moisture is less variable than near the soil surface. Weeds germinate at various times throughout the season depending on environmental cues such as moisture availability and soil temperature. Weeds produce prolific numbers of seeds which may lie dormant for very brief (2 weeks) or very long (30-50 yrs) periods before germination. Weed seeds are distributed by wind, rain, birds, and mechanical harvesting equipment.
Pest Distribution and Importance:
Annual grasses infest approximately 98% of all corn acres. Many of these are controlled with preemergence herbicide applications and tillage. While usually not as competitive as broadleaf weed species, annual grasses can reduce crop yields when significant populations are present. This is particularly true in dry years, where competition for moisture early in the season can be critical for corn development. See Appendix C for a description of the relative importance of various weeds in the Midwest.
Foxtails (Setaria spp.)
There are three important foxtail species: giant foxtail (Setaria faberi), yellow foxtail (Setaria
glauca), and green foxtail (Setaria viridis). At least one of these species can be found in nearly any corn
field in the North Central Region. While low populations cause little crop competition, because of seed
production an unchecked population can quickly become a severe problem. A primary control method
for foxtail spp. is the application of preemergence grass herbicides. These provide early season control,
reducing early season competition with the corn. Robust white foxtail (Setaria viridis var. robusta-albaSchreiber) and purple robust foxtail (Setaria viridis var. robusta-purpurea) at two additional species
that can be found in MN with regularity.
Woolly Cupgrass (Eriochloa villosa [Thunb.] Kunth.)
Woolly cupgrass is a relatively new and potentially serious weed problem in the states of Iowa, Illinois, Wisconsin and Minnesota. Its spread has increased rapidly in the last 10 to 15 years. This annual grass weed demonstrates biological, biochemical, and morphological characteristics that make it economically damaging and adds to the difficulty in developing effective management strategies. Woolly cupgrass is a prolific seed producer. This seed tends to germinate earlier and at higher populations than many other annual grass weeds. Woolly cupgrass has demonstrated tolerance to most herbicides commonly used for control of annual grasses in corn.
Fall Panicum (Panicum dichotomiflorum)
Fall panicum is a summer annual that grows best in warm, wet, fertile soils. The plant tillers profusely and in late August and September the tillers open and scatter hard-coated seeds. These seeds may remain viable for years, and fall panicum is most often a problem in reduced or no-till fields whose undisturbed soils are favorable for germination. Fall panicum has shown some tolerance to atrazine, and can be a serious grass weeds in the region. Fall panicum is generally a serious weed south of Interstate 90.
Wild Proso Millet (Panicum miliaceum)
Wild proso millet is a summer annual that tends to be more common in no-till fields and in areas where popcorn and sweet corn production are prevalent.
Barnyardgrass (Echinochloa crusgalli)
This summer annual germinates from 0 to 4 inches deep in the soil. The seeds remain viable for several years, and plants may emerge throughout the summer. Barnyardgrass is most troublesome in low, moist, warm areas.
Field Sandbur (Cenchrus pauciflorus, also C. longispinus)
Field sandbur is a summer annual weed common in sandy soils. The bur of field sandbur can injure the mouth of feeding cattle.
Crabgrass spp. (Digitaria spp.)
A warm season grass most often troublesome in the southern region of the Corn Belt. The plants root at the nodes and due to a high root to shoot ratio may be very competitive where moisture is limiting. May be most severe during the late part of the growing season after herbicides have degraded and/or holes remain in the canopy. Tillage and row cultivation also help control.
Shattercane (Sorghum bicolor)
Shattercane is an annual grass that is found primarily in cultivated fields where it reseeds itself. Since all sorghums are members of the same species and can hybridize, shattercane is often found in greater populations were sorghums are grown. It is more prevalent in the southern portion of the Corn Belt and hardly ever found north of Interstate 80. Shattercane outcrosses with other sorghum types and is known for developing resistance to ALS type herbicides.
Wild Oat (Avena fatua)
Commonly found in the norther portion of the corn belt. It tends to be more serious in areas where small grains are grown.
As noted in the table below, both pre and post emergence herbicides are used for annual grass control. Four classes of herbicide active ingredients are used pre-emergence; triazines (simazine, atrazine), acetamides (alachlor, metolachlor, dimethenamid, and acetochlor), dinitroaniline (pendimethalin), and thiocarbamates (EPTC, and butylate). In addition, glyphosate is sometimes use as a burndown herbicide prior to plant, especially on no-till corn. EPTC and butylate have decreased in use for corn production due to increased use of conservation tillage and the availability of other viable options. For control ratings of each weed for each listed herbicide or non-chemical management practice see the table at the end of this section.
Photosystem I inhibitor (Triazines).
Inexpensive and have excellent crop safety. They are also readily available. Tend to be synergistic with many other herbicides. They perform reliably and have good handling characteristics. Can be combined with many other herbicides and some insecticides. Most have long lasting residual control of many weeds that may result in carryover concern to rotational crops. They also have the potential for contamination of nearby water. Have high potential for weed resistance development.
Atrazine (Many, in Marksman, Laddok). Growers have vast experience with all formulations. Atrazine is economical and cost effective. Under right conditions it will control some annual grasses post emergence. An expansion of post applied options (tank and pre-mixes) might reduce per acre rates. The REI is 12hrs and the PHI is 21d.
Simazine (Princep) Simazine is cost effective, and has better grass control than atrazine although it has an overall narrower spectrum of control than atrazine. Cannot be tank mixed with as many products as atrazine nor is it as available as atrazine. More persistent than atrazine (more carryover concerns). Almost no simazine is used in MN, WI, SD and ND. The REI is 12hrs and the PHI is NA.
Root/Shoot Inhibitor (Acetamides).
Generally good crop safety (exc. Acetochlor, see below). They have good grass control and the likelihood of weed resistance exceedingly small. They have good window of application prior to planting but weed control is weather dependent. Water contamination from runoff/leaching is a concern.
Alachlor (Micro-tech) Not much used-has been replaced by products with better efficacy and less environmental concern. The REI is 12hrs and the PHI is NA.
Metolachlor (Dual II Mag) The level of control is good to excellent. It is used on no-till acres because it can be applied early. Slightly more persistent than acetochlor but not as good on small seeded broadleaf weeds. Poor on woolly cupgrass. The REI is 12hrs and the PHI is 30d.
Dimethenamid (Outlook) Control of grasses is good. The REI is 12hrs And the PHI is 40d.
Acetochlor (Harness/Surpass, in FulTime & several others) Good control of most grasses and small seeded broadleaf weeds but timing is important. Marginal control of sandbur and woolly cupgrass. Good on yellow foxtail and waterhemp and other small seeded broadleaves. Crop safety can be variable depending on weather. FulTime, as a post treatment, has the potential for some crop injury, other acetochlor formulations also have some potential for crop injury. The REI is 12hrs and the PHI is 21d.
Flufenacet (Define) The REI is 12 hrs and the PHI is not indicated. Can be used up to 45 days before planting at 21 oz product per acre.
Mitosis Inhibitor (Dinitroanilines)
Pendimethalin (Prowl/Pentagon). Pendimethalin is inexpensive. The likelihood of weed resistance development is low. Good grass and small seeded broadleaf weed control. Crop injury can occur but replant options may be restricted. The REI is 12hrs and the PHI is NA.
Bleaching
Isoxaflutole (Balance) The level of control is good but only for low grass pressure. Better than metolachlor and acetochlor on woolly cupgrass. Poor on yellow foxtail. Label restrictions due to water contamination concerns. Some propensity for crop injury. The REI is 12hrs and the PHI is NA. Not registered for use in MN, WI, or MI.
Mesotrione (Callisto) New compound and its activity is little known. The REI is 12hrs and the PHI is 30d.
Shoot Inhibitor (Thiocarbamates)
EPTC (Eradicane) Butylate (Sutan Plus) Excellent grass and small seeded broadleaf weed control. Likelihood of weed resistance development is low. Crop injury potential (yield suppression). Requires mechanical incorporation (cannot use in no is till, some reduced till). Weed tolerance resulting from enhanced (accelerated) biodegradation in some fields. The REI is NA and the PHI is NA. The use of EPTC and butylate has declined to the point that many dealers no longer carry these products. Specialists expect these herbicides to generally become unavailable across the region.
ALS Inhibitors (Sulfonylureas)
Rimsulfuron + Thifensulfuron (Basis) @ 0.33 to 0.62 oz product per acre. The REI is 4 hrs and the PHI is NA when used pre-emergence. May result in crop injury if used on crops treated with organophosphate insecticides.
EPSP Synthase Inhibition
Glyphosate (Roundup). Broad spectrum with low to moderate cost. Except for glyphosate tolerant hybrids, use is strictly for burndown of existing vegetation prior to planting and for spot application to localized troublesome weeds after emergence. There is a concern because not all markets take a GMO crop There is potential for weed resistance development (although low if properly managed). Drift injury potential for adjacent non-RR crops and non-crop plants. Glyphosate is easy to use and safe for the environment. Tolerance/resistance developing in some weeds and there are concerns about rotation of modes of action. Time of day can affect efficacy. The REI is 4hrs and the PHI is 7d.
Glutamine Synthetase Enzyme Inhibition
Glufosinate (Liberty) The level of control is depends on coverage but can be good. Control is also good for most annual broadleaves and woolly cupgrass. Must be applied to tolerant hybrids if used after crop emerges. The REI is 12hrs and the PHI 70d.
For control ratings of each weed for each listed herbicide or non-chemical management practice see the table at the end of this section.
ALS inhibitors (Sulfonylureas).
Generally easy to use. They have the potential for crop injury and a possible interaction with OP insecticides and may need to use drop nozzles during appl to reduce injury (depends on crop stage). High potential for weed resistance development. Cost may be higher than many herbicides.
Nicosulfuron (Accent). Excellent post grass control (sometimes no other alternative). Good control of sandbur and good for rescue treatments. There is a potential for resistance development in weeds. Costly relative to other products. Crop injury potential present but low if timing properly managed. The REI is 4hrs and the PHI is 30d.
Primisulfuron (Beacon, in NorthStar, in Exceed, in Spirit). Primarily for broadleaf weed control. Combination products are broader spectrum (NorthStar, Exceed, Spirit). Generally poor grass weed control except for shattercane. There is a broad application window. May need to use drop nozzles for some applications to minimize injury potential. The REI is 12hrs and the PHI is 45-60d.
Nicosulfuron + clopyralid+ rimsulfuron+flumetsulam (Accent Gold) @ 2.9 oz per acre. The REI is 48 hrs and the product can be applied up to the 12 inch stage for corn. Controls both grasses and broadleaf weeds.
Rimsulfuron + Thifensulfuron (Basis) @ 0.33 oz product per acre. The REI is 4 hrs and the PHI is 30 days. May result in crop injury if used on crops treated with organophosphate insecticides.
Nicosulfuron+Rimsulfuron (Steadfast) Primarily grass weed control. Application timing is critical for best weed control. The REI is 4hrs and the PHI is variable.
Nicosulfuron+Rimsulfuron+Atrazine (Basis Gold) @ 14 oz per acre. The REI is 12hrs.
Foramsulfuron (Option) The REI is 12 hours and the PHI is 45d for forage and 70d for grain. The use rate is 1.5 oz product per acre.
Biology and Life Cycle:.
Although perennial grasses and nutsedges produce seed each year the primary mechanism of reproduction is through vegetative propagation. Tillage can be an effective mechanism of controlling perennial grasses but when done improperly may further distribute the weed throughout the field and exacerbate the problem. Quackgrass is a cool weather plant and grows aggressively early in the spring and in the fall. The other perennials listed tend to grow more actively during the late spring and summer.
Pest Distribution and Importance:
Perennial grasses were once a severe problem in corn production prior to herbicides and when pasture was a standard part of the crop rotation. With the introduction of effective herbicides and decline in pasture rotations, many perennial grasses have declined in importance. See Appendix C for a description ranking of weed importance in the Midwest.
Quackgrass (Elytrigia repens)
Quackgrass is a perennial grass that spreads by rhizomes. These rhizomes are effectively spread by tillage, increasing the scope of the population in a field. Tillage is an effective control by depleting food reserves and bringing rhizomes to the surface.
Wirestem Muhly (Muhlenbergia frondosa)
Wirestem muhly is a perennial grass that reproduces by seeds and underground rhizomes. It is native to the Midwest. It was not considered a common row crop weed until the 1950's when serious infestations developed in cultivated fields. Delayed seedbed preparation will help control wirestem muhly in corn by bringing rhizomes to the soil surface to dry out.
Johnsongrass (Sorghum halepense)
Johnsongrass produces large rhizomes that can be spread throughout the field making it difficult to contain and control. Johnsongrass is more common in the southern portions of the Corn Belt and is seldom found north of I-80.
Yellow Nutsedge (Cyperus esculentus)
Yellow nutsedge causes the most severe perennial weed infestations and is quite serious across the region. It reproduces from tubers as the seed does not survive overwintering, and tubers can adapt to almost any soil type and conditions. Tubers germinate at depths of up to 12 inches and may remain viable for up to three years in many soils. .
Pre-emergence herbicide control of shattercane, nutsedges, and perennial grasses is generally with the use of EPTC or butylate. In addition, nutsedge can be suppressed by the acetamide herbicides, especially acetochlor. Roundup can also be used if the grasses are present in the field and growing prior to planting or if the grasses are actively growing after the crop is removed. For quackgrass, nutsedge, and Johnsongrass, tillage is useful.
For control ratings of each weed for each listed herbicide or non-chemical management practice see the table at the end of this section..
Root/Shoot Inhibitor (Acetamides).
Generally good crop safety (exc. Acetochlor, see below). They are included in this section primarily for their control of nutsedges. The level of control of nutsedges for the products listed below should be listed as fair to good. The likelihood of weed resistance exceedingly small. They have good window of application prior to planting but weed control is weather dependent. Water contamination from runoff/leaching is a concern.
Alachlor (Micro-tech) Not much used-has been replaced by products with less environmental concern. The REI is 12hrs and the PHI is NA.
Metolachlor (Dual II Mag) Slightly more persistent than acetochlor. The REI is 12hrs and the PHI is 30d.
Dimethenamid (Outlook) The REI is 12hrs And the PHI is 40d.
Acetochlor (Harness/Surpass, in FulTime & several others) Crop safety can be variable depending on weather. FulTime, as a post treatment, has the potential for some crop injury, other acetochlor formulations also have some potential for crop injury. The REI is 12hrs and the PHI is 21d.
Flufenacet (Define) The REI is 12 hrs and the PHI is not indicated. Can be used up to 45 days before planting at 21 oz product per acre.
Shoot Inhibitor (Thiocarbamates)
EPTC (Eradicane) Butylate (Sutan Plus) Has good control of nutsedges and some control or suppression of other perennial grasses. Likelihood of weed resistance development is low. Crop injury potential (yield suppression). Requires mechanical incorporation (cannot use in no is till, some reduced till). Weed tolerance resulting from enhanced (accelerated) biodegradation in some fields. The REI is NA and the PHI is NA. The use of EPTC and butylate has declined to the point that many dealers no longer carry these products. Specialists expect these herbicides to generally become unavailable across the region.
EPSP Synthase Inhibition
Glyphosate (Roundup). Broad spectrum weed control. Low to moderate cost. Potential for weed resistance development (although low if properly managed). Drift to adjacent crops and non-crop plants. The REI is 4hrs and the PHI is 7d.
Post emergence shattercane and perennial grass control is generally achieved by the use of Accent, Beacon, or Exceed or Spirit. As indicated below for the specific products the hazard for these chemicals is crop injury and an inability to use them where certain OP insecticides have been used on the crop. Nutsedge may be controlled by Permit or by the use of Basagran or Laddok.
For control ratings of each weed for each listed herbicide or non-chemical management practice see the table at the end of this section.
ALS inhibitors (Sulfonylureas). Easy to use. There is crop injury potential and a high potential for weed resistance development. Possible interaction with OP insecticides resulting in crop injury. Need to use drop nozzles during application to reduce crop injury. Cost is higher than most other herbicides
Nicosulfuron (Accent). Excellent post grass control (sometimes no other alternative). Crop injury potential (hybrid sensitivity) is common. The REI is 4hrs and the PHI is 30d.
Primisulfuron (Beacon, in NorthStar, in Exceed, in Spirit). Primarily broadleaf weed control. Combination products are broader spectrum (NorthStar, Exceed, Spirit). Poor grass weed control generally. The REI is 12hrs and the PHI is 45-60d.
Halosulfuron (Permit) Primarily broadleaf weed control with poor grass weed control. Application timing is critical. The REI is 12hrs and the PHI is 30d.
Biology and Life Cycle:.
Broadleaf weeds germinate at soil depths from 1/8th of an inch to 3 or 4 inches. Seed size and dormancy are the controlling factors for when and where these seeds emerge. Large seeded broadleaf weeds have greater seed food reserves and can emerge from greater soil depths where moisture is less variable than near the soil surface. Weeds germinate at various times throughout the season depending on environmental cues such as moisture availability and soil temperature. Weeds produce prolific numbers of seeds which may lie dormant for very brief (2 weeks) or very long (30-50 yrs) periods before germination. Weed seeds are distributed by wind, rain, birds, and mechanical harvesting equipment.
Pest Distribution and Importance:
Each of the weeds listed below has its own distribution range and importance. The importance of various weeds is highly dependent upon the prevailing attitudes and herbicide use practices. As herbicide use patterns change weed species change as well. See Appendix C for a description ranking of weed importance in the Midwest.
Eastern Black Nightshade (Solanum ptycanthum)
This summer annual can produce thousands of berries; each berry contains up to 50 seeds. While nightshade is generally not considered a serious pest in the Corn Belt, severe infestations in individual fields do occur. Tillage and row cultivation are effective for early, newly emerged seedlings.
Common Cocklebur (Xanthium strumarium)
Common cocklebur is a summer annual weed. Its seeds are spread by attaching to animal fur or by tillage or harvesting equipment. Cocklebur is a serious competitor for moisture. Cultivation and tillage will all help control cocklebur establishment.
Common Lambsquarters (Chenopodium album)
Common lambsquarters produce numerous small seeds which germinate after an overwintering process. Optimal temperature for germination is 70F, but can germinate between 40 to 94, which suggests early germination capabilities. Survival is favored by rains that dilute or leach herbicides from the soil surface.
Common Ragweed (Ambrosia artemisiifolia)
Common ragweed is a summer annual that is favored by moist soils and can be a serious problem in individual fields. Control of common ragweed with tillage or row cultivation is effective in controlling small seedlings.
Giant Ragweed (Ambrosia trifida)
Wet weather favors giant ragweed, and this summer annual may be a severe problem in isolated fields. The seeds of giant ragweed may remain viable in the soil for several years. Small seedlings can be controlled with row cultivation and tillage.
Jimsonweed (Datura stramonium)
Jimsonweed produces several hundred hard-coated seeds per plant that may remain viable in the soil for years. This summer annual grows best under warm temperatures and moist soils. Jimsonweed infestations harm soybean crops via competition for water, especially in dry years. The shade of its leaves in shorter crops increases yield loss due to decreased nutrient uptake. Jimsonweed also contains the alkaloids, atropine, hyoscyamine, and hyoscine, which are toxic. Even small amounts of jimsonweed can cause harvest problems. Jimsonweed, which is easily controlled by a number of herbicides, has declined in importance over the last 10 to 15 years. It does not tend to occur as a problem in fields north of Interstate 80.
Kochia (Kochia scoparia)
Kochia is similar to common lambsquarters in many respects. It produces numerous small seeds and can germinate early in the season. Kochia has also developed resistance to a number of herbicides including triazines and ALS compounds. Although not distributed as widely as lambsquarters, kochia has been expanding from small infestations started along rail and road systems where seed has been carried in.
Morningglories (Ipomoea spp.)
Tall morningglory and ivyleaf morningglory are the two major annual morningglory species found in the Corn Belt. Morningglories are generally not a problem north of Interstate 80. The seeds of these summer annuals may survive for several years in soil. Infestations are most common in moist soils along river bottomland, but these plants can be found most anywhere in the state. Annual morningglories adapt to crops by vining about the crop, so shading by the canopy is not particularly successful in reducing growth. Newly emerged seedlings can be controlled by tillage and cultivation, but this may result in conditions that favor emergence by weeds deeper in the soil profile. After vines begin to twine about the stems of the crop, cultivation may not be as effective.
Pennsylvania Smartweed (Polygonum pensylvanicum)
This summer annual grows best on wet soils and is widely distributed across the Midwest. Smartweed emerges early in the spring and can be a severe problem if tillage is delayed to wet soils, as seedbed preparation may result in transplanting larger plants rather than destroying them.
Pigweeds (Amaranthus retroflexus, A. hybridus, A. powellii)
Pigweeds are prolific seed producers, and one plant can produce over 100,000 seeds in one growing season. The seeds of this plant may remain viable for years. Pigweeds are a problem in no-till systems because undisturbed soils favor germination of the minuscule seeds, and the debris keeps the field moist and allows for extended germination. Other favorable germination locations are where excess nitrogen is available, and where no soil applied herbicides have been used. Localized populations of some biotypes of pigweed have shown triazine or acetolactate synthase (ALS)-inhibitor resistance.
Velvetleaf (Abutilon theophrasti)
Velvetleaf is the most significant annual broadleaf weed in most corn production and is most damaging in the central part of the region. Velvetleaf is a serious competitor for moisture in drought conditions. Cultivation can somewhat control velvetleaf when used in the early season.
Waterhemp (Amaranthus tuberculatus, A. rudis)
Common waterhemp is a native species and is a serious weed problem throughout the Corn Belt. Changes in agricultural practices that favor this weed include reductions in tillage, herbicide selection, simplified crop rotations, and recent weather patterns. There are also many indigenous factors that have contributed to the increase in common waterhemp populations. These include seedling emergence late in the growing season, high seed production and an ability to germinate from shallow soil depths. Control of common waterhemp has become increasingly difficult due to resistance to many common herbicides. Waterhemp has demonstrated cross-resistance to herbicides with the ALS inhibition mode of action, as well as to triazine compounds.
Wild Sunflower (Helianthus annuus)
A weed that has become more predominant over the last 10 years. It germinates in the top 2 to 3 inches of soil and can grow to a height of 8 to 10 feet.
Pre-Emergence Control of Annual Broadleaf Weeds
Soil applied herbicides need to be in place and evenly distributed throughout the top 1 to 2 inches of soil at the time of weed emergence for adequate uptake and maximum effect. Under conditions of high rainfall many pre-emergence herbicides may be too diluted or leached out of this soil zone and rendered ineffective. Under very dry conditions, pre-emergence herbicides may not have been leached into the soil far enough to have the substantial contact necessary for weed death. Other broadleaf weeds produce small seeds, such as pigweeds, lambsquarters, kochia, and nightshade. Many of these weeds germinate throughout the season in response to soil wetting provided by occasional rainfall. Pre-emergence herbicides, which have short soil persistence, may not adequately control the late flushes of germinating weeds.
For control ratings of each weed for each listed herbicide or non-chemical management practice see the table at the end of this section.
Photosystem I Inhibitor (Triazines).
Inexpensive and have excellent crop safety. They are also readily available. Tend to be synergistic with many other herbicides. They perform reliably and have good handling characteristics. Can be combined with many other herbicides and some insecticides. Most have long lasting residual control of many weeds that may result in carryover concern to rotational crops. They also have the potential for contamination of nearby water. Have high potential for weed resistance development.
Atrazine (Many, in Marksman, Laddok). Extremely good for post emergence weed control especially when combined with other herbicides. Growers have vast experience with all formulations. Atrazine is economical and cost effective. Under right conditions it will control some annual grasses post emergence. An expansion of post applied options (tank and pre-mixes) might reduce per acre rates. The REI is 12hrs and the PHI is 21d.
Simazine (Princep) Simazine is cost effective, and has better grass control than atrazine although it has an overall narrower spectrum of control than atrazine. Cannot be tank mixed with as many products as atrazine nor is it as available as atrazine. More persistent than atrazine (more carryover concerns). The REI is 12hrs and the PHI is NA. Almost no simazine is used in MN, WI, SD and ND.
Root/Shoot Inhibitor (Acetamides).
Generally good crop safety (exc. Acetochlor, see below). They have good grass control and the likelihood of weed resistance exceedingly small. They have good window of application prior to planting but weed control is weather dependent. Water contamination from runoff/leaching is a concern.
Alachlor (Micro-tech) Not much used-has been replaced by products with better efficacy and less environmental concern. The REI is 12hrs and the PHI is NA.
Metolachlor (Dual II Mag) The level of control is good to excellent. It is used on no-till acres because it can be applied early. Slightly more persistent than acetochlor but not as good on small seeded broadleaf weeds. Poor on woolly cupgrass. The REI is 12hrs and the PHI is 30d.
Dimethenamid (Outlook) Control of grasses is good. The REI is 12hrs And the PHI is 40d.
Acetochlor (Harness/Surpass, in FulTime & several others) Good control of most grasses and small seeded broadleaf weeds but timing is important. Marginal control of sandbur and woolly cupgrass. Good on yellow foxtail and waterhemp and other small seeded broadleaves. Crop safety can be variable depending on weather. FulTime, as a post treatment, has the potential for some crop injury, other acetochlor formulations also have some potential for crop injury. The REI is 12hrs and the PHI is 21d.
Flufenacet (Define) The REI is 12 hrs and the PHI is not indicated. Can be used up to 45 days before planting to at planting at 21 oz product per acre.
Mitosis Inhibitor (Dinitroanilines)
Pendimethalin (Prowl/Pentagon). Pendimethalin is inexpensive. The likelihood of weed resistance development is low. Good grass and small seeded broadleaf weed control. Crop injury can occur. Replant options may be restricted. The REI is 12hrs and the PHI is NA.
Bleaching
Isoxaflutole (Balance) The level of control is good but only for low grass pressure. Better than metolachlor and acetochlor on woolly cupgrass. Poor on yellow foxtail. Label restrictions due to water contamination concerns. Some propensity for crop injury. The REI is 12hrs and the PHI is NA. Not registered for use in MN, WI, or MI.
Mesotrione (Callisto) New compound and its activity is little known. The REI is 12hrs and the PHI is 30d. (Lumax, Camix) New combination products for use pre-emergence.
ALS Inhibitors (Sulfonylureas)
Rimsulfuron + Thifensulfuron (Basis) @ 0.33 to 0.62 oz product per acre. The REI is 4 hrs and the PHI is NA when used pre-emergence. May result in crop injury if used on crops treated with organophosphate insecticides.
Sulfonylurea+ Growth Regulator
Clopyralid+flumetsulam (Hornet) Some soil residual activity. Can be mixed with atrazine to increase spectrum of activity. The REI is 48hrs and the PHI is 85d.
Shoot Inhibitor (Thiocarbamates)
EPTC (Eradicane) The REI is NA and the PHI is NA.
Butylate (Sutan Plus) Excellent small seeded broadleaf weed control. Likelihood of weed resistance development is low. Crop injury potential (yield suppression). Requires mechanical incorporation (cannot use in no is till, some reduced till). Weed tolerance resulting from enhanced (accelerated) biodegradation in some fields. The REI is NA and the PHI is NA. The use of these herbicides has declined to the point their use is difficult to track. Specialists indicate that dealers may soon stop carrying them if they already haven't.
EPSP Synthase Inhibition
Glyphosate (Roundup). Broad spectrum with low to moderate cost. Except for glyphosate tolerant hybrids, use is strictly for burndown of existing vegetation prior to planting and for spot application to localized troublesome weeds after emergence. There is a concern because not all markets take a GMO crop There is potential for weed resistance development (although low if properly managed). Drift injury potential for adjacent non-RR crops and non-crop plants. Glyphosate is easy to use and safe for the environment. Tolerance/resistance developing in some weeds and there are concerns about rotation of modes of action. Time of day can affect efficacy. The REI is 4hrs and the PHI is 7d.
Glutamine Synthetase Enzyme Inhibition
Glufosinate (Liberty) The level of control is depends on coverage but can be good. Control is also good for most annual broadleaves and woolly cupgrass. Must be applied to tolerant hybrids if used after crop emerges. The REI is 12hrs and the PHI 70d.
As mentioned above, several flushes of broadleaf weeds can occur throughout the season. Although there are no post-emergence broadleaf herbicides with true "residual" activity some herbicides do provide a modicum of control through soil activity. These herbicides include post applications of Atrazine and dicamba. Though the trend for increasing use of post applied herbicides continues, concerns about crop injury and drift to off-target crops or plants remains a hindrance. A new product and new chemistry is Callisto (mesotrione). Since it is newly registered for corn little is known of the advantages and disadvantages other than it has potential for broadleaf weed control. However, new chemistries are always welcome from the perspective of managing resistant weed development.
For control ratings of each weed for each listed herbicide or non-chemical management practice see the table at the end of this section.
Sulfonylurea+ Growth Regulator
Clopyralid+flumetsulam (Hornet) Some soil residual activity. Can be mixed with atrazine to increase spectrum of activity. The REI is 48hrs and the PHI is 85d.
Semicarbazone
Diflufenzopyr+dicamba (Distinct) Application timing is critical. Potential for crop injury is unknown. Good for bindweeds and Canada thistle. May be an alternative for atrazine in tank mixes. The REI is 12hrs and the PHI is 32-72d.
Growth Regulator
Inexpensive. Broad spectrum of control of broadleaf weeds and some perennial broadleaf weeds. Potential for crop injury. Preharvest interval sometimes too long for effective use.
Drift to adjacent crops and non is crop plants.
2,4-D (Many) Control is very rate dependent. Cost effective. Crop safety and drift concerns. Works good for a burndown especially with Roundup. Breaks down rapidly in the environment. The REI is 48hrs and the PHI is 7d.
Dicamba (Clarity, Banvel, in NorthStar, in Marksman). Some residual activity in soil.
Performance spectrum enhanced by addition of atrazine. Good on toothed spurge and thistles.
Potential for brace root deformation under high temperature and humidity conditions. The REI is
12hrs and the PHI will vary based on product.
Clopyralid (Stinger) The REI is 12 hours and the PHI is 2d. The use rate is 0.25 to 0.66 pt/acre.
ALS Inhibitors (Sulfonylureas)
Generally easy to use. They have the potential for crop injury and a possible interaction with OP insecticides and may need to use drop nozzles during appl to reduce injury (depends on crop stage). High potential for weed resistance development. Cost may be higher than many herbicides.
Nicosulfuron (Accent). Excellent post grass control (sometimes no other alternative). Good control of sandbur and good for rescue treatments. There is a potential for resistance development in weeds. Costly relative to other products. Crop injury potential present but low if timing properly managed. The REI is 4hrs and the PHI is 30d.
Primisulfuron (Beacon, in NorthStar, in Exceed, in Spirit). Primarily for broadleaf weed control. Combination products are broader spectrum (NorthStar, Exceed, Spirit). Generally poor grass weed control except for shattercane. There is a broad application window. May need to use drop nozzles for some applications to minimize injury potential. The REI is 12hrs and the PHI is 45-60d.
Nicosulfuron + clopyralid+ rimsulfuron+flumetsulam (Accent Gold) @ 2.9 oz per acre. The REI is 48 hrs and the product can be applied up to the 12 inch stage for corn. Controls both grasses and broadleaf weeds.
Rimsulfuron + Thifensulfuron (Basis) @ 0.33 oz product per acre. The REI is 4 hrs and the PHI is 30 days. May result in crop injury if used on crops treated with organophosphate insecticides.
Nicosulfuron+Rimsulfuron (Steadfast) Primarily grass weed control. Application timing is critical for best weed control. The REI is 4hrs and the PHI is variable.
Nicosulfuron+Rimsulfuron+Atrazine (Basis Gold) @ 14 oz per acre. The REI is 12hrs.
Foramsulfuron (Option) The REI is 12 hours and the PHI is 45d for forage and 70d for grain. The use rate is 1.5 oz product per acre.
PPO Inhibitor
Carfentrazone (Aim) Relatively new product and new chemistry. Advantages and disadvantages are not all known at the time of this writing. It does have a relatively narrow weed control spectrum. However, new chemistries are always welcome from the perspective of managing resistant weed development. REI is 12hrs and the PHI is not indicated.
Cell Membrane Disruptor
Flumiclorac (Resource) The REI is 12 hours and the PHI is 28d. The use rate is 4 to 8 fl oz product.
Photosystem II Inhibitors
Effective on small weeds especially when used in combination with other herbicides. Primarily for broadleaf weed control.
Pyridate (Tough). In some situations may cause crop injury. Applicators must be extremely careful with sprayers using air-assist booms. The REI is 12hrs and the PHI is 68d.
Bromoxynil (Buctril, in Buctril-Atrazine). Moderate to good crop safety. Requires good coverage for control. No soil residual for late emerging weeds. Needs tank mixing with other products for acceptable activity on many weeds. The REI is 12hrs and the PHI is 30d.
Bentazon (Basagran, in Laddok). Good crop safety. The REI is 12hrs and the PHI is 21d.
EPSP Synthase Inhibition
Glyphosate (Roundup). Broad spectrum of control of grass and broadleaf weeds (also perennials). It has a good application window. Safe for the environment. Must be applied to tolerant corn hybrids if applied in-season. Low to moderate cost. Time of day of application affects efficacy. Potential for weed resistance development (although low if properly managed). Drift to adjacent crops and non-crop plants. The REI is 4hrs and the PHI is 7d.
Glutamine Synthetase Enzyme Inhibition
Glufosinate (Liberty) Must be applied to tolerant corn hybrids. The REI is 4hrs and the PHI is 70d.
Biology and Life Cycle:.
While perennial weeds do produce seeds, the majority of plants listed propagate through vegetative means. Most perennial weeds begin growth early in the season before crops are planted and may also have a very active period of growth after the crop has been harvested. Tillage can be effective for controlling many perennial weeds but it may also distribute viable rhizomes, roots, and tubers throughout the field if done improperly.
Pest Distribution and Importance:.
The occurrence of perennial broadleaf weeds is highly dependent on the tillage regime used in corn production. Since most perennial broadleaf weeds do not tolerate tillage, these weeds are more of a problem in reduced tillage and no-till operations. Currently all of the weeds listed below could be considered a more serious problem than they were 5 to 10 years ago. See Appendix C for a description ranking of weed importance in the Midwest.
Common Milkweed (Asclepias syrica L)
This perennial weed reproduces by seeds and adventitious buds that sprout from underground roots. Seedlings produce vegetative buds 18-21 days after germination, and seeds may remain viable for up to three years. Seeds may germinate from as deep as 2 inches in the soil, and undisturbed fields or fields with reduced tillage and moist soils are favored. Problems with common milkweed have been increasing due to the decrease in tillage and row cultivation.
Canada Thistle (Cirsium arvense)
Canada thistle is a perennial weed with a vigorous, rhizom-like root system. Propagation is by rootstock and seeds; only female plants produce seed. Preplant tillage and row cultivation can control small seedlings but are less effective in controlling plants arising from rootstocks.
Field Bindweed (Convolvulus arvensis) and hedge bindweed (Calystegia sepium)
These weeds are vining weeds commonly found in both cultivated and no-till fields. These weeds can rapidly engulf corn rows in vines reducing corn growth and yield. The extensive mass of vines also makes harvest very difficult.
Hemp Dogbane (Apocynum cannabium)
This perennial weed is capable of regrowth from perennating rootstock within six weeks of emergence. The underground root system may extend laterally 20 feet per year and downward as far as 14 feet. The central portion of the Corn Belt is usually most severely infested with dogbane with very little infestations north of Interstate 90. Tillage can reduce dogbane infestations, but is ineffective once populations are established.
Swamp Smartweed (Polygonum coccineum Muhl. ex Willd)
Swamp smartweed is commonly found in low, wet areas of fields. Because of an extensive root system it is a strong competitor with corn and difficult to eradicate. Because of it's similarity to Pennsylvania smartweed, an annual, many producers incorrectly identify this weed.
Bigroot Morningglory (Ipomoea pandurata)
Bigroot morningglory is becoming more common. It produces a tuber that can reach eight inches in diameter and several feet deep. When the new vines emerge they are purplish in color. Control almost invariably will require many repeated treatments. This weed is primarily a problem in fields south of Interstate 80.
Pokeweed (Phytolacca americana)
Pokeweed is becoming more important as a weed throughout the eastern section of the Corn Belt. It tends to be hard to kill and severe infestations can cause contamination of grain that can result in its rejection by elevators.
Pre and Post Emergence Control of Perennial Broadleaf Weeds
While much of the effort to control perennial weeds takes place before the crop is planted or after it has been harvested, effective control of perennial weeds often necessitates control efforts during the cropping season as well. The control ratings for some of the more common perennial broadleaf weeds are included in a table at the end of this section. Other perennial broadleaf weeds, such as pokeweed, hedge bindweed, and Jerusalem artichoke may also be present in some fields, but are less prevalent.
The control ratings given for perennial weeds tend to be more subjective than those for annual weeds. For example, although a rating of "Good" for control of an annual weed typically suggests 85 percent or better control of a weed, a rating of "Good" for perennial weeds might indicate anywhere from 60% to 90% dieback. The variability in rating perennial weeds arises from the fact that there are fewer studies to determine control, there are fewer products and control measures available with which to compare, and that perennial weeds typically re-sprout from root stock soon after dieback. It is generally agreed that multiple treatments in a season, which include a combination of herbicides and mechanical means of control, are necessary to reduce perennial weed populations and obtain what is otherwise termed "Good" control.
EPSP Synthase Inhibition
Glyphosate (Roundup) Fair for common milkweed control, hemp dogbane, and swamp smartweed. Good for Canada thistle and field bindweed control and generally a good broad spectrum herbicide. It has low to moderate cost and is safe for the environment. Must be used on tolerant crop when used post emergence. Potential for weed resistance development (although low if properly managed). Drift to adjacent crops and non-crop plants can cause injury. The REI is 4hrs and the PHI is 7d.
Growth Regulator
Generally inexpensive and broad spectrum, (controls more than perennials). It has the potential for crop injury, especially when mixed with other growth regulators. Required preharvest interval sometimes too long for effective use. Drift injury potential to adjacent crops and non-crop plants.
2,4-D (Many). The ester formulation is particularly effective for perennial but can cause additional concern with drift. Canada thistle (Fair), Field Bindweed (Good), and morningglory family (Fair). It can also be used to accelerate the uptake of glyphosate for improved control of other broadleaf perennial weeds. It is cost effective and good for use in burndown applications and as a tank mix with Roundup. Breaks down rapidly in the environment. Control is rate dependent. The REI is 48hrs and the PHI is 7d.
Dicamba (Clarity, Banvel, in NorthStar, in Marksman). Some residual activity in soil for annuals. Good crop tolerance. Good on Canada thistle, musk thistle, and field bindweed. Potential for brace root injury under high temperature and humidity conditions. The REI is 12hrs and the PHI varies depending on product.
Photosystem II Inhibitors
Bentazon (Basagran, in Laddok). Effective on Canada thistle (Good). Good crop safety. The REI is 12hrs and the PHI is 21d.
Sulfonylurea+ Growth Regulator
Clopyralid+flumetsulam (Hornet) Some soil residual activity. Can be mixed with atrazine to increase spectrum of activity. The REI is 48hrs and the PHI is 85d.
Growth Regulator
Clopyralid (Stinger) The REI is 12 hours and the PHI is 2d. The use rate is 0.25 to 0.66 pt/acre.
Clopyralid + 2,4-D (Curtail) The REI is 48 hours and the PHI is 30d. For use in MN, KS, NE, and ND. The use rate is 2pt/acre.
Tillage
Can be quite effective if planting is delayed until early sprouting occurs, although multiple deep tillage events may be required. The soil erosion that results from tillage may preclude its use on many soils. Timing is critical, if done improperly tillage may result in the spread of rhizomes or root stock and proliferate the problem
Biology and Life Cycle:.
Winter annual weeds start their growth in the fall and complete their life cycle in the spring, often bearing seed in May or June. While discing, plowing, or field cultivation tillage is effective for all winter annuals, no-till and conservation tillage fields must rely on herbicides for control. Heavy populations of winter annual weeds can sap the moisture from the soil and slow or reduce germination of the crop.
Pest Distribution and Importance:
A number of winter annual weeds can be present in fields throughout the Midwest with the most common of these being henbit and chickweed. Some winter annuals are more prevalent across the northern portion of the Corn Belt, while others such as bluegrass and bromegrass tend to be more of a problem across the southern section of Missouri, Illinois, Indiana and Ohio. Weeds present in the field early in the season may attract damaging insects and provide an environment for egg laying. Cover crops tend not to be used in MN, WI, ND or SD. See Appendix C for a descriptive ranking of weeds in the Midwest.
Common Chickweed (Stellaria media)
A common weed which produces prolific amounts of seed and a thick mat of low vegetative growth. Can remove much soil moisture and, if untreated, can seriously affect crop establishment and growth in dry years. Less of a problem north of Interstate 80. Not a problem north of Interstate 90.
Horseweed (Marestail) (Conyza canadensis)(previously Erigeron canadensis)
This weed is becoming much more common throughout the Midwest due to reduced tillage. It produces a large amount of seed that is wind borne. Resistant biotypes of this weed to glyphosate have been identified.
Henbit (Lamium amplexicaule)
This plant is a low growing (5 to 9 inches) winter annual. It can produce a thick mat of growth early in the season and pull needed moisture from the soil. Less of a problem north of Interstate 80. Not a problem north of Interstate 90.
Mustards
Mustard species include field pennycress (Thlaspi arvense), wild mustard (Brassica kaber), tansy mustard (Descurainia pinnata), shepherd's-purse (Capsella bursa-pastoris), yellow rocket (Barbarea vulgaris), and the pepperweeds (Lepidium spp.) Although a number of herbicides may control some mustard species, the presence of mature (large) mustards in the fields early in the season often limits which herbicides may be applied. Though usually less aggressive than henbit and common chickweed in terms of population expansion, they are serious competitors with crops.
Brome Grasses (Bromus spp.)
Winter annual brome grasses include downy brome, Japanese brome, and cheat. If left uncontrolled these grasses will continue to pose a competitive threat to the crop.
Bluegrass (Poa annua)
Bluegrass can become more of a problem under continuous no-till. Though populations do not grow at an explosive rate, control without tillage can be difficult.
Grass Cover Crops
Grass cover crops include winter annual grains planted to protect the soil and build soil tilth and at times, more established sods from conservation plantings being converted to cropland. The former may include barley, rye, and wheat while the latter may include ryegrass, orchardgrass, perennial bromegrasses, fescue and timothy. Cover crops are seldom used in MN, WI, ND or SD.
Legume Cover Crops
Alfalfa, clovers, and vetches are typically used as cover crops or as part of a forage mix with grasses in conservation plantings that are being converted to cropland. Where forage mixes are present a broadspectrum herbicide, or a tank mix of two herbicides capable of killing both the grass and the legume, will be necessary for control. Cover crops are seldom used in MN, WI, ND or SD.
The following herbicides are commonly used for burndown of winter annual weeds or cover crops. Various combinations of these products may be used depending on the weed species present and the size of the weeds. Added to this list could be metolachlor, although it must be applied early enough to actually prevent winter annuals from germinating or allow time for the herbicide to move into the root zone for absorption through the root system.
Photosystem I Inhibitor (Triazines).
Inexpensive and have excellent crop safety. They are also readily available. Tend to be synergistic with many other herbicides. They perform reliably and have good handling characteristics. Can be combined with many other herbicides and some insecticides. Most have long lasting residual control of many weeds that may result in carryover concern to rotational crops. They also have the potential for contamination of nearby water. Have high potential for weed resistance development.
Atrazine (Many, in Marksman, Laddok). Extremely good for post emergence weed control especially when combined with other herbicides. Growers have vast experience with all formulations. Atrazine is economical and cost effective. Under right conditions it will control some annual grasses post emergence. An expansion of post applied options (tank and pre-mixes) might reduce per acre rates. The REI is 12hrs and the PHI is 21d.
Simazine (Princep) Simazine is cost effective, and has better grass control than atrazine although it has an overall narrower spectrum of control than atrazine. Cannot be tank mixed with as many products as atrazine nor is it as available as atrazine. More persistent than atrazine (more carryover concerns). The REI is 12hrs and the PHI is NA.
EPSP Synthase Inhibition
Glyphosate (Roundup). Broad spectrum with low to moderate cost. Except for glyphosate tolerant hybrids, use is strictly for burndown of existing vegetation prior to planting and for spot application to localized troublesome weeds after emergence. There is a concern because not all markets take a GMO crop There is potential for weed resistance development (although low if properly managed). Drift injury potential for adjacent non-RR crops and non-crop plants. Glyphosate is easy to use and safe for the environment. Tolerance/resistance developing in some weeds and there are concerns about rotation of modes of action. Time of day can affect efficacy. The REI is 4hrs and the PHI is 7d.
Glutamine Synthetase Eenzyme Inhibition
Glufosinate (Liberty) The level of control is depends on coverage but can be good. Control is also good for most annual broadleaves and woolly cupgrass. Must be applied to tolerant hybrids if used after crop emerges. The REI is 12hrs and the PHI 70d.
Growth Regulator.
Generally inexpensive and broad spectrum, (controls more than perennials). It has the potential for crop injury, especially when mixed with other growth regulators. Required preharvest interval sometimes too long for effective use. Drift injury potential to adjacent crops and non-crop plants.
2,4-D (Many). The ester formulation is particularly effective for perennial but can cause additional concern with drift. Canada thistle (Fair), Field Bindweed (Good), and morningglory family (Fair). It can also be used to accelerate the uptake of glyphosate for improved control of other broadleaf perennial weeds. It is cost effective and good for use in burndown applications and as a tank mix with Roundup. Breaks down rapidly in the environment. Control is rate dependent. The REI is 48hrs and the PHI is 7d.
Dicamba (Clarity, Banvel, in NorthStar, in Marksman). Some residual activity in soil for annuals. Good crop tolerance. Good on Canada thistle, musk thistle, and field bindweed. Potential for brace root injury under high temperature and humidity conditions. The REI is 12hrs and the PHI varies depending on product.
Tillage.
Tillage is an effective method of controlling winter annual weeds and cover crops. However, tillage may not always be practical due to conservation requirements or soil conditions. The soil erosion that results from tillage may preclude its use on many soils
A number of weed biotype populations have been identified as having resistance to one or more herbicide classes. Those most commonly found are waterhemp, lambsquarters, kochia, and pigweeds. In addition, resistant biotypes of common ragweed, cocklebur, shattercane, velvetleaf and giant foxtail have been found in some areas. The herbicide modes of action that have resulted in the most rapid development of resistant populations include those that have been used with the greatest frequency for weed control in corn and soybeans. This would include the triazines (translocated photosynthetic inhibitors) and the ALS inhibitors (sulfonylureas and imadazilinones). There is considerable concern about the potential development of resistance to glyphosate as it also has become widely used within the last 5 years.
The difficulty in dealing with herbicide resistant weeds is often that the presence of such weeds necessitates the use of a more robust and more expensive approach to weed control. Since whole groups of compounds are no longer effective many individual products within those groups will no longer be efficacious. Control often rests on a strategy of crop rotation (to permit rotation of herbicides) and herbicide combinations.
The development of resistant weed biotypes can be delayed or postponed indefinitely through the proper selection of herbicides, tillage, and equipment and field sanitation.
No further information was indicated for herbicide resistant weeds.
Table 4. Weed Control Ratings from Various Weed Management Practices
| Blank is poor control or unknown
(Product/practice not used) F is fair control G is good control E is excellent control |
1. Barnyardgrass 2. Wild proso Millet 3. Crabgrass |
4. Fall Panicum
5. Foxtails 6. Woolly Cupgrass 7. Field Sandbur |
1. Shattercane
2.Johnsongrass
3. Quackgrass 4. Nutsedge |
1.Morningglory
2.BurCucumber 3. Cocklebur 4. Jimsonweed |
1. Common Ragweed
2. Giant ragweed 3.Smartweed 4. Wild SunFlower 5. Velvetleaf |
1.Pigweed/waterhemp
2. Lambsquarter 3. Kochia 4. Nightshade |
Winter Annuals
1. Bromegrass
2.Henbit/chickweed 3. Horseweed 4. Mustards | |||||||||||||||||||||
| PPI & PRE | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 |
| Atrazine 90DF | G | F | F | F | F | F | F | G | F | G | E | E | F | E | F | F | E | G | G | G | F | G | G | E | ||||
| Princep-simazine | G | F | F | G | G | G | G | G | G | F | F | F | E | G | F | G | G | G | G | E | ||||||||
| Micro-Tech-alachlor | E | G | E | G | G | F | F | F | G | F | G | |||||||||||||||||
| Dual II Mag-metolachlor | E | G | E | E | G | F | F | F | F | G | G | G | G | F | G | |||||||||||||
| Frontier-Outlook dimethenamid | G | F | E | E | G | F | F | F | G | F | G | |||||||||||||||||
| Surpass/Harness-acetochlor | E | G | E | E | G | G | F | F | F | G | F | E | G | G | ||||||||||||||
| Axiom-flufenacet | G | G | E | G | F | F | F | F | G | G | F | |||||||||||||||||
| Prowl-pendimethalin | E | F | G | G | G | G | G | G | G | F | ||||||||||||||||||
| Balance-isoxaflutol | G | F | F | G | G | F | G | G | G | G | G | G | G | G | F | |||||||||||||
| Epic-flufenacet-isoxaflutol | E | G | F | G | F | G | G | G | G | E | G | G | G | |||||||||||||||
| Hornet-clopyralid+flumetsulam | G | G | F | G | G | G | G | G | G | G | ||||||||||||||||||
| Eradicane/Sutan-EPTC&Butylate | E | G | E | E | E | G | G | G | G | F | G | G | G | F | F | G | ||||||||||||
| Python-flumetsulam | F | G | G | G | E | G | G | F | ||||||||||||||||||||
| Callisto-mesotrione | F | G | F | G | G | G | G | |||||||||||||||||||||
| POST | ||||||||||||||||||||||||||||
| 2,4-D amine | E | E | F | G | G | F | G | G | G | G | F | F | G | E | ||||||||||||||
| Clarity-dicamba | E | G | E | G | E | G | G | G | F | G | G | G | G | E | F | F | ||||||||||||
| Distinct | F | E | F | E | G | E | G | G | G | G | G | G | G | G | ||||||||||||||
| Stinger | E | G | E | G | F | G | G | |||||||||||||||||||||
| Accent-nicosulfuron | E | G | G | G | G | G | E | E | G | G | G | G | G | G | ||||||||||||||
| Accent Gold | E | G | G | G | F | G | G | G | F | G | F | G | G | G | G | G | G | G | G | F | F | F | ||||||
| Aim-carfentrazone' | F | G | F | F | G | G | G | G | G | |||||||||||||||||||
| Beacon-primisulfuron | F | E | G | G | F | 6 | G | G | G | G | G | G | G | F | G | 6 | G | G | ||||||||||
| Basis | G | F | F | G | F | G | F | F | F | G | G | G | G | G | F | |||||||||||||
| Basis Gold | G | F | G | G | F | F | G | F | F | G | F | G | G | G | F | G | G | G | G | G | G | F | ||||||
| Exceed/Spirit- | E | F | F | F | G | E | E | G | G | G | G | G | E | G | G | G | ||||||||||||
| Lightning | G | G | G | G | G | G | E | G | F | E | G | F | F | G | G | G | E | G | G | G | ||||||||
| NorthStar-primisulfuron+dicamba | F | F | F | F | E | F | G | E | E | G | E | G | G | E | G | G | G | E | G | |||||||||
| Permit-halosulfuron | G | F | F | E | G | E | G | F | E | G | G | F | ||||||||||||||||
| Hornet | G | G | G | G | G | G | G | G | F | F | F | F | ||||||||||||||||
| Atrazine+Oil | G | F | F | F | F | F | F | F | G | F | E | E | E | G | E | G | E | E | G | G | E | |||||||
| Buctril-Contour-bromoxynil | F | F | G | E | F | G | G | G | G | F | E | G | E | |||||||||||||||
| Tough 5EC-pyridate | G | G | G | G | G | F | F | F | G | G | F | G | ||||||||||||||||
| Roundup-glyphosate (Burndown) | E | E | E | E | E | E | E | G | G | G | G | G | E | E | E | G | G | G | E | G | E | E | E | E | E | E | E | E |
| Liberty | G | G | G | F | G | G | G | G | G | F | E | E | G | G | G | G | G | G | F | G | G | |||||||
| Callisto-mesotrione | G | G | G | G | G | G | G | E | G | G | G | |||||||||||||||||
| Celebrity | G | G | G | G | G | G | E | G | G | G | G | G | G | G | G | E | G | G | E | G | G | G | ||||||
| Marksman-dicamba+atrazine | G | G | E | G | E | F | E | G | G | E | E | G | G | G | E | E | E | |||||||||||
| Basagran-bentazon | G | G | G | G | G | G | F | F | G | F | F | |||||||||||||||||
| Laddok | G | G | G | G | G | G | G | E | G | G | G | G | ||||||||||||||||
| Adjust Plant/harvest date | ||||||||||||||||||||||||||||
| Tillage | F | F | F | F | G | G | G | G | ||||||||||||||||||||
| Paraquat | F | G | F | |||||||||||||||||||||||||
Table 5. Herbicide Used on Field Corn, Brand Names, REI & And the PHIs, and Percent of Corn
Acres Treated in 2000.
| Chemical | Brand Names | Re-Entry Interval |
Pre Harvest Interval |
% Acres Treated |
| hrs | days | |||
| 2,4-D Amine | 48 | 7 | 8 | |
| Acetochlor | Surpass, Harness, Doubleplay | 12 | 21 | 25 |
| Alachlor | Micro-Tech | 12 | 4 | |
| Atrazine | atrazine, Extrazine, Marksman, Contour, | 12 | 21 | 68 |
| Bentazon | Laddok, Basagran, | 12 | 21 | 2 |
| Bromoxynil | Buctril+atrazine, Buctril | 12 | 30 | 4 |
| Butylate | Sutan+ | |||
| Carfentrazone | Aim | 12 | 1 | |
| Clopyralid | Stinger, Scorpion, Hornet | 12-48 | 40-85 | 9 |
| Cyanazine | Bladex, Extrazine | 12 | 0 | |
| Dicamba | Celebrity, NorthStar, Celebrity B&G, | 12 | 29 | |
| Diflufenzopyr | Distinct | 12 | 32-72 | 3 |
| Dimethenamid | Frontier, Outlook | 12 | 40 | 7 |
| EPTC | Eradicane | 1 | ||
| Flumetsulam | Hornet, Python, Accent Gold | 48 | 85 | 10 |
| Flumiclorac | Resource | 12 | 28 | |
| Foe5043 | Axiom 68DF | 12 | 2 | |
| Glufosinate | Liberty, Liberty ATZ | 12 | 70 | 2 |
| Glyphosate | Roundup Ultra | 4 | 7 | 9 |
| Halosulfuron | Permit | 12 | 30 | |
| Imazapyr | Lightning | 12 | 45 | 2 |
| Imazethapyr | Contour, Lightning, Resolve | 12 | 45 | 3 |
| Isoxaflutol | Balance | 12 | 3 | |
| Mesotrione | Callisto | |||
| Metolachlor | Dual II | 12 | 30 | 12 |
| S-Metolachlor | Magnum | 16 | ||
| Nicosulfuron | Accent, Basis Gold, Accent Gold, Celebrity | 4 | 30 | 15 |
| Pendimethalin | Prowl/Pentagon | 12 | 3 | |
| Primisulfuron | Exceed, NorthStar, Beacon, Spirit | 12 | 45-60 | 9 |
| Prosulfuron | Spirit, Exceed | 12 | 60 | 4 |
| Pyridate | Tough, Stinger | 12 | 68 | 5 |
| Rimsulfuron | Basis, Basis Gold | 4 | 30 | 9 |
| Simazine | Princep | 12 | 2 |
Principal Editor and Contact:
David R. Pike
808 Stratford Dr.
Champaign, IL 61821
217 352 6405
airs-inc@"no-spam"insightbb.com
Contributors:
Michael Gray Dept of Crop Sciences, Univ of IL graym@"no-spam"mail.aces.uiuc.edu
Bryan Jensen Dept of Entomology, Univ of WI bmjense1@"no-spam"facstaff.wisc.edu
Rich Pope Dept of Entomology, IA State Univ ropope@"no-spam"iastate.edu
Lowell Sandell Entomology Dept, Univ of KY lsandell@"no-spam"uky.edu
George Smith MO Dept of Ag, Columbia, MO George_Smith@"no-spam"mail.mda.state.mo.us
Bob Hartzler Dept of Agron, Iowa State Univ hartzler@"no-spam"iastate.edu
Brad Ruden SD State Univ, Brookings, SD ruden.brad@"no-spam"ces.sdstate.edu
Bob Wright Entomologist, Univ of NE-Clay Center rwright@"no-spam"unlnotes.unl.edu
Dave Regher Kansas State Univ. dregehr@"no-spam"oznet.ksu.edu
Jeff Gunsolus Univ of Minnesota gunso001@"no-spam"umn.edu
Doug Jardine Kansas State Univ. JARDINE@"no-spam"plantpath.ksu.edu
Alex Martin Weed Scientist, University of Nebraska armartin@"no-spam"unlnotes02.unl.edu
Remove "no-spam" from the email addresses to make them active.
Appendix A Results of Weed Distribution and Severity Surveys
Three different pest ranking systems have been used and include: ranking by farmer opinion, ranking by prevalence in acreage as determined by scouting, and ranking via the estimates of discipline specialists.
The table below contains estimates of weed severity as estimated by all three methods. The first column showing numerical data was taken from weed specialists from the major corn producing states in 1997. The second column of numerical data was taken from a survey of corn producers in the North Central States. The last column of numerical data is the percent of fields with observed weed infestations as noted from crop consulting records in northern IL and eastern IA.
| Weeds | Ordinal rank of weeds
by crop loss. 1997 survey of specialists in 16 corn producing states A |
Ordinal rank of weeds
by severity. 1992 survey of growers in 12 midwestern states B |
Percent of fields infested 1991-1995 scouting records from N. Illinois & E. Iowa C | |
| Amaranthus spp | pigweeds | 1 | 4 | 11 |
| Abutilon theophrasti | velvetleaf | 2 | 5 | 1 |
| Sorghum bicolor | shattercane | 3 | 26 | |
| Setaria faberi* | giant foxtail | 4 | 1 | 2 |
| Apocynum cannabinum | hemp dogbane | 5 | 22 | 4 |
| Chenopodium album | common lambsquarters | 6 | 8 | 5 |
| Polygonum pensylvanicum | Pennsylvania smartweed | 7 | 11 | 8 |
| Ambrosia trifida | giant ragweed | 8 | 2 | 9 |
| Ipomoea spp | morningglory spp. | 9 | 12 | 15 |
| Sorghum halepense | Johnsongrass | 10 | 24 | |
| Setaria lutescens | yellow foxtail | 11 | ||
| Xanthium strumarium | common cocklebur | 12 | 6 | 10 |
| Agropyron repens | quackgrass | 13 | 13 | 20 |
| Eriochloa villosa | woolly cupgrass | 14 | 14 | |
| Digitaria sanguinalis | large crabgrass | 15 | 19 | |
| Solanum spp | nightshade spp | 16 | 14 | 18 |
| Panicum dichotomiflorum | fall panicum | 17 | 18 | |
| Echinochloa crus-galli | barnyardgrass | 18 | 15 | |
| Kochia scoparia | kochia | 19 | 20 | |
| Setaria viridis | green foxtail | 20 | ||
| Cirsium arvense | Canada thistle | 21 | 9 | 12 |
| Ambrosia artemisiifolia | common ragweed | 22 | 3 | 21 |
| Cyperus spp | nutsedges | 23 | 10 | 6 |
| Panicum miliaceum | witchgrass | 24 | ||
| Mustard spp | mustards | 25 | 17 | |
| Helianthus annuus | common sunflowers | 26 | 16 | |
| Digitaria ischaemum | smooth crabgrass | 27 | ||
| Datura stramonium | jimsonweed | 28 | 21 | |
| Asclepias syriaca | common milkweed | 7 | 3 | |
| Convolvulus spp. | bindweeds | 19 | 19 | |
| Salsoli kali | Russian thistle | 23 | ||
| Cenchrus pauciflorus | field sandbur | 25 | ||
| Taraxicum officinale | dandelion | 7 | ||
| Ampelamus albidus | honeyine milkweed | 13 |
* All foxtail species were included in the farmer opinion survey under one listing.
A 1997 Agricultural Information Services Ltd. 9 Bovingdon Rd, London SW6 2AP. Proprietary study of pest
management on 40 US crops.
B Aref, Suzanne, and D. R. Pike. 1998. Midwest Farmers' Perceptions of Crop Pest Infestation. Ag. J. 90:6, p819-825
C Pike, D. R. and D. Harms. 1998. The occurrence and densities of weeds in Illinois and Iowa as noted from Crop
Scouting Records, Unpublished.
Appendix B: Results of Insect Distribution and Severity Surveys
| Insects | Scientific Name | Ranked by
aggregate insect
losses.
1997 survey of specialists in 16 corn producing states A |
Ranked by
opinion of
severity. 1992 survey of growers in 12 midwestern states B |
| Northern corn rootworm | Diabrotica barberi | 1 | 2 |
| Western corn rootworm | Diabrotica virgifera ** | 2 | 2 |
| European corn borer | Ostrinia nubilalis* | 3 | 1 |
| Black cutworms | Agrotis ypsilon | 4 | 3 |
| Spider mites | Tetranychus spp. | 5 | 6 |
| White grubs | Phyllophaga spp.*** | 6 | 5 |
| Cutworm | Euxoa spp. | 7 | 3 |
| Southwestern corn borer | Diatraea grandiosella* | 8 | 1 |
| Wireworms | Melanotus spp.*** | 9 | 5 |
| Corn ear worm | Helicoverpa zea | 10 | |
| Seed corn maggot | Delia platura | 11 | |
| Grasshoppers | Melanoplus spp. | 4 | |
| Aand the PHIds | Aand the PHIdidae spp. | 6 |
* not separated in grower survey
** not separated in grower survey
*** not separated in grower survey
A 1997 Agricultural Information Services Ltd. 9 Bovingdon Rd, London SW6 2AP. Proprietary study of pest
management on 40 US crops.
B Aref, Suzanne, and D. R. Pike. 1998. Midwest Farmers' Perceptions of Crop Pest Infestation. Ag. J. 90:6, p819-825
Appendix C : Results of Plant Disease Distribution and Severity Survey
| Disease | Scientific Name | Ranked by
aggregate
disease losses.
1997 survey of specialists in 16 corn producing states A |
| Seedling/root/stalk rot | Fusarium | 1 |
| Ear/seedling/stalk rot | Gibberella spp | 2 |
| Anthracnose stalk/leaf | Colletotrichum spp | 3 |
| Gray leaf spot | Cercospora zeae-maydis | 4 |
| Seedling rots/damping off | Pythium spp | 5 |
| Eyespot | Kabatiella zeae | 6 |
| Diplodia ear and stalk rot | Diplodia maydis | 7 |
| Nematodes | Various species | 8 |
| Smuts | Ustilago maydis | 9 |
| Rusts | Puccinia spp | 10 |
| Leaf blights | Helminthosporium spp | 11 |
| Maize dwarf mosaic virus | MDMV | 12 |
| Aspergillus ear and kernel rot | Aspergillus flavus | 13 |
A 1997 Agricultural Information Services Ltd. 9 Bovingdon Rd, London SW6 2AP. Proprietary study of pest management on 40 US crops.
Appendix D Pest Infestation Estimates
Estimates of Treatment, Infestations, and Losses from Various Field Corn Pests in the US Corn Belt. Losses do not include cost of control. 1997 data courtesy of AIS Ltd., London, GBr. A
| A. Percent of all US. corn acres treated with a pesticide having some efficacy for the pest | B. Percent of all US. corn acres infested but not treated (or treated but retains infestation) | C.Average
annual losses
on acreage in
column B.
($ Millions) |
D. States contributing estimates. (No estimates were obtained from S. Dakota for any pest and weed information was not obtained from Missouri.) | ||
| Aspergillus flavus | Aspergillus | 0 | 12.3 | 13 | Ks,ne |
| Cercospora zeae-maydis | Gray leaf spot | 2.8 | 16.3 | 213 | Il,in,ia,ks,ky,mi,ne,oh,pa |
| Colletotrichum framinicola | Anthracnose leaf blight/stalk rot | 9.9 | 12.4 | 215 | In,ky,mn,oh,wi,ny,pa |
| Diplodia maydis | Diplodia ear rot | 9.9 | 40.4 | 84 | Il,ky,mn,ne,oh,in,wi |
| Fusarium moniliforme | Seedling/stalk/root/ear/kernel rot | 32.9 | 65.4 | 556 | In,ks,ne,oh,wi,ia,mi,ny,pa |
| Gibberella zeae | Stalk rot/ear rot | 9.9 | 35.7 | 310 | In,iq,oh,pa,wi |
| Exserohilum turcicum | Northern corn leaf blight | 0.5 | 15.7 | 22 | In,ne,pa,il,ks,ny,oh,wi |
| Aureobasidium zeae | Eyespot | 0.6 | 15.8 | 86 | Ia,ne,wi |
| MDMV | Maize Dwarf Mosaic Virus | 0.0 | 12.4 | 15 | Ne,tx |
| Puccinia maydis | Common rust | 0.6 | 13.0 | 26 | Ia,ne,tx |
| Pythium spp | Seed/seedling/root rot | 47.6 | 45.8 | 129 | Il,ia,ny,pa,wi |
| 1,672 | |||||
| Agrotis ipsilon | Cutworm | 10.7 | 14 | 80 | Il,in,ia,ks,ky,mi,mn,mo,ne,oh,pa,wi |
| Diabrotica spp | Corn Rootworm species | 43.9 | 41.4 | 640 | Il,in,ia,ks,ky,mi,mo,nd,ne,ny,pa,wi |
| Diatraea grandiosella | Southwestern corn borer | 1.6 | 2.6 | 29 | Ks,ky,mo |
| Euxoa spp | Dark sided cutworm | 1.2 | 2.6 | 11 | Nd,mo,wi |
| Melanotus spp | Wireworm | 1.0 | 3.0 | 21 | Ks,mi,mo,wi |
| Ostrinia nubilalis | European corn borer | 19.8 | 22.1 | 578 | Il,in,ia,ks,ky,mi,mn,mo,nd,ne,oh,pa,wi |
| Phyllophaga spp | White Grub | 1.4 | 1.1 | 26 | Ks,mi,mo,nd,wi |
| Tetranychus spp | Spider Mites | 1.2 | 2.2 | 42 | Ks,ne |
| 1,431 | |||||
| Abutilon theophrasti | Velvetleaf | 72.4 | 44.8 | 147 | Il,in,ia,ks,ky,mi,mn,ne,ny,oh,pa,wi |
| Elytrigia repens | Quackgrass | 11.1 | 6.4 | 36 | Il,in,ia,mi,mn,nd,ne,ny,oh,pa,wi |
| Amaranthus retroflexus | Redroot pigweed | 62.8 | 21.9 | 15 | Il,in,ia,ky,mi,mn,oh |
| Amaranthus spp | Other pigweed species | 23.0 | 18.1 | 145 | Ks,mn,nd,ne,ny,pa,wi |
| Ambrosia artemisiifolia | Common ragweed | 38.1 | 27.0 | 6 | Il,in,ia,ky,mi,mn,nd,ne,ny,oh,pa,wi |
| Ambrosia trifida | Giant ragweed | 32 | 9.8 | 56 | Il,in,ia,ky,mn,ne,oh,wi |
| Apocynum cannabiunm | Hemp dogbane | 4.0 | 5.7 | 62 | Ks,mi,ne,pa |
| Chenopodium album | Common Lambsquarters | 77.2 | 24.4 | 53 | Il,in,ia,ky,mi,mn,nd,ne,ny,oh,pa,wi |
| Cirsium arvense | Canada thistle | 5.3 | 4.5 | 18 | Mi,mn,nd,oh,pa |
| Convolvus spp | Bindweeds | 1.7 | 0.5 | 6 | Ny,oh,mi |
| Cyperus esculentus | Yellow nutsedge | 33.1 | 20.7 | 10 | Il,in,ia,ks,ky,mi,mn,ne,ny,oh,pa,wi |
| Datura stramonium | Jimsonweed | 18.1 | 18.0 | 3 | Il,in,ia,mi,ne |
| Digitaria ischaemum | Smooth crabgrass | 19.4 | 19.4 | 3 | Il,in,ky,mi,ne,ny,wi |
| Digitaria sanguinalis | Large crabgrass | 36.7 | 26.1 | 37 | Il,in,ia,ks,ky,mi,mn,ne,ny,oh,wi |
| Echinochloa crus-galli | Barnyardgrass | 2.3 | 2.2 | 21 | Ne,ny |
| Eriochloa vllosa | Woolly Cupgrass | 6.5 | 3.0 | 34 | Ia,mn,wi |
| Helianthus annuus | Common sunflower | 1.8 | 0.6 | 4 | Ks,nd,ne |
| Ipomoea spp | Morningglory species | 28.8 | 21.6 | 30 | Il,in,ia,ks,ky,ne,oh |
| Kochia scoparia | Kochia | 5.1 | 5.5 | 20 | Ks,nd,ne |
| Panicum dichotomiflorum | Fall panicum | 34.8 | 24.6 | 27 | Il,in,ia,ky,mi,ne,ny,oh,pa,wi |
| Panicum miliaceum | Wild proso millet | 5.1 | 2.5 | 16 | Mn,nd,wi |
| Polygonum pensylvanicum | Pensylvania smartweed | 51.1 | 30.2 | 54 | Il,in,ia,ky,mi,mn,ne,ny,oh,wi |
| Setaria faberi | Giant foxtail | 81.9 | 44.6 | 91 | Il,in,ia,ks,ky,mi,mn,ne,ny,oh,wi |
| Setaria lutescens | Yellow foxtail | 8.4 | 6.6 | 48 | Ks,mn,ne |
| Setaria spp | Foxtail (unspecified) | 2.5 | 1.7 | 9 | Nd,pa |
| Setaria viridis | Green foxtail | 23.4 | 2.5 | 10 | Ia,mn,ny,wi |
| Solanum ptycanthum | E. Black nightshade | 30.6 | 22.2 | 21 | Il,ia,ky,mi,,mn,nd,ne,oh,wi |
| Sorghum halepense | Johnsongrass | 12.4 | 10.3 | 47 | Il,in,ks,ky,ne,oh,pa |
| Sorghum bicolor | Wild cane | 16.8 | 13.6 | 139 | Il,in,ia,ks,ky,ne,oh, |
| Xanthium strumarium | Common cocklebur | 52.0 | 29.8 | 37 | Il,in,ia,ks,ky,mi,mn,nd,ne,oh |
| 1,205 |
A 1997 Agricultural Information Services Ltd. 9 Bovingdon Rd, London SW6 2AP. Proprietary study of pest management on 40 US crops.
Appendix E. Corn Rootworm Distribution and Importance:
Western Corn Rootworm (WCR) overcoming crop rotation -
Portions of northern and central Illinois, northern Indiana, southern Michigan, and western Ohio have
been affected by a dramatic change in WCR beetle behavior. Previously, WCR adults laid eggs primarily in
cornfields. Now, a variant form of WCR beetle lays a majority of its eggs in soybean fields, and has lost its
preference to lay eggs in corn. By laying eggs in soybean fields, economic root damage to corn the following
season can occur. This behavioral change has virtually eliminated the benefit of crop rotation as a rootworm
management tactic in the most severely affected regions of the problem area. Therefore, growers are now using
soil insecticides in continuous cornfields, as well as first-year cornfields (primarily fields with a corn/soybean
rotation).
At this point, the reason for this dramatic change in behavior is unknown.
Northern Corn Rootworm (NCR) extended diapause -
First-year cornfields in areas of Minnesota, Iowa, Wisconsin, and South Dakota have been extensively
damaged by NCR that exhibits an extended diapause trait. Extended diapause is the condition that allows NCR
eggs to remain dormant in the soil for not only one, but two winters, as well as through one complete growing
season. NCR populations exhibiting this trait, in areas that incorporate crop rotation for rootworm control, have
experienced significant rootworm larval damage in first-year corn. Growers in these problem areas are also using
soil insecticides in continuous and first-year cornfields.
Problematic areas of NCR extended diapause and WCR eggs being laid in soybean.
soybean.