Crop Profile for Cotton in Alabama

Prepared: December, 1999
Revised: September, 2001

The year 1997 was an unusual one for Alabama’s cotton producers. Cool temperatures early in the season, especially in north Alabama, led to poor stands and stunted growth of young plant seedlings. Despite problems, the remaining cotton acreage turned out a decent crop of 550,000 bales with an average yield of nearly 600 pounds of lint per acre. (2)

• Alabama ranked 11th in the United States, producing 2.9% of the United States’ production total of 18,977,000 bales of cotton in 1997. (1)
• 535,000 acres of cotton were planted in Alabama in 1997. (4)
• 550,000 bales of cotton were harvested on 442,000 acres in Alabama in 1997. (4)
• The average price per pound was $.68 for a production value of approximately $179,520,000. (3)
• 196,000 tons of cottonseed averaged $111 per ton for a production value of $21,312,000. (3)
• Cost of production is estimated at $546 per acre. (25)

Production Regions

There are five loosely defined cotton production regions in the state: (1) Tennessee Valley that stretches across the northern tier of counties; (2) northeast Alabama; (3) central counties that include Talladega, Shelby, Chambers, Lee, Tallapoosa, Macon, Montgomery, Elmore, Autauga, Dallas, Pickens, Hale and Marengo (this is not an exhaustive list); (4) Wiregrass counties of southeast Alabama; and (5) southwest Alabama that includes the Gulf Coast counties. Each region may include several soil textures and growing environments.

In 1997, cotton was produced in 25 counties in Alabama. Leading cotton-producing counties were Monroe, Escambia, Geneva, Colbert, Lawrence, Houston, Baldwin, Cherokee, Lauderdale and Covington. (4, 5)

• Soil types — Cotton is produced on several soil textures ranging from sandy loam to heavy clay soils. The best soils for production have a minimum pH of 5.5 on sandy soils and 5.8 on clay soils and are well drained. In soils that develop a hardpan that impedes taproot development, producers often break the pan using a subsoiler or paraplow. Most fields are tilled in the fall with a turning plow and prepared in the spring for planting using a field cultivator or chisel plow. The trend is towards reduced tillage operations.
• Irrigation practices — Most of the fields in Alabama are not irrigated; however, the trend is towards more irrigation in northern counties.
• Land preparation — Land preparation for planting is conventional in a majority of the crops across the state. Conservation tillage practices are used on 15% to 20% of the acreage each year and include no-till planting into old crop stubble or small grain residue or planting into a small area prepared using a row till implement.
• Planting times - The most common planting dates for cotton in the state are April 10 through May 1 in north Alabama, April 20 through May 10 in central Alabama, and April 20 through May 20 in south Alabama. Harvest generally begins in mid September and is completed in mid December in most years. Planting rates are based on the desired number of plants per foot. The most common planting rates are 15 pounds of seed per acre in northern counties, 10 to 12 pounds per acre in central counties and 8 to 10 pounds per acre in southern counties. Since the total number of seeds per pound varies in each variety, the planting rate will also vary.
• Variety selection - Variety selection depends on the characteristics desired in herbicide tolerance (conventional, Roundup Ready and Buctril resistant), insect tolerance (Bt or conventional), growth habit (upright and tall or bushy and shorter) and maturity (early, medium or full season). Some varieties are selected based on production system (irrigated or dryland, conventional rows or ultra narrow row, etc.). Insect and/or herbicide tolerant varieties are being utilized on a majority of the acreages in the state.
• Varieties grown - The major variety grown in Alabama in 1997 was Deltapine, followed by Sure Grow and other varieties including Paymaster, Stoneville and Hyperformer. (8)

Cotton is attacked by a number of damaging insect species. Certain pests occur on every acre every year while others are more sporadic in occurrence. Insects that reach economic levels on most acres each season are thrips, plant bugs, aphids, bollworms, tobacco budworms and stinkbugs. Other insects such as cutworms, grasshoppers, beet armyworms, fall armyworms, European corn borers, southern armyworms, yellow striped armyworms, cabbage loopers, soybean loopers, spider mites, whiteflies, western flower thrips and fleahoppers vary in occurrence from year to year or by geographical area. Several of these sporadic insects reach damaging levels in certain areas each season. In fact, it is not uncommon for multiple economic pests to occur in fields at the same time.

Cotton fruits over an extended period during the crop production season. This period typically extends for approximately 3 months. The crop is susceptible to injury from one or more insects from the time it emerges as a seedling until the youngest harvestable fruit is mature, a period of about 120 to 140 days.

Historically, insect pressure has varied due to the geographical location within the state. Plant bugs and spider mites are a greater problem in the northern area of the state, probably due to more abundant wild hosts. Migratory pests such as fall and beet armyworms and other pests that overwinter in greater numbers during mild winters are more abundant in the southern areas. Certain pests are somewhat weather related. Most of these are more common in dry seasons. Examples in this category are spider mites, whiteflies and beet armyworms. On the other hand, cutworms are associated with cool, wet springs. One management practice, reduced tillage, has resulted in more widespread cutworm problems in recent years.

Most cotton insects feed on the developing fruit. This means that relatively low levels of insects can cause economic losses. In most instances, any damage to the fruit causes a resulting yield loss since the cotton plant can only compensate by producing smaller and later maturing fruit. With the cost of production inputs and the price of the commodity today, the highest possible yield must be obtained for cotton production to be a profitable enterprise.

Other insects (thrips and cutworms) that feed on or damage seedling plants are also important since cotton needs to develop rapidly once it emerges. The few insects that feed primarily on foliage (loopers and southern armyworms) are not as economic unless they occur in high numbers. Thresholds for these pests are set high so that insecticide inputs will not be required unless absolutely necessary.

Table 1. Percentage of Acres Infested with Pests in a Typical Season

A factor that has greatly impacted the pest spectrum on cotton is the introduction of genetically altered varieties (Bts). Bt cotton gives 100% control of tobacco budworms and European corn borers, about 75% suppression of bollworms and some suppression of beet armyworms. On the other hand, Bt cotton replaces from two to eight or more insecticide applications targeted for bollworms and budworms. This also serves to suppress or control plant bugs and fall armyworms. The chemistry often replaced by Bt cotton is the pyrethroid class.

Where conventional cotton is planted, the dominant pests are tobacco budworms and bollworms. Other widespread insects such as plant bugs, armyworms and stinkbugs are suppressed by pyrethroids targeted for bollworms. If budworms are the target insect and Tracer (Spinosad) chemistry is utilized, then a phosphate or pyrethroid must be tank mixed for these other insects. When Bt cotton is planted, plant bugs, fall armyworms, bollworms and stinkbugs become the primary target insects. In this situation, either a phosphate or pyrethroid is the appropriate choice of chemistry.

Most of the new chemistry under development for lepidopterous pests is very selective in nature and will give no control of insects such as plant bugs and stinkbugs. Examples of this new chemistry expected in the marketplace within the next few years are Steward (Dupont), Denim (Novartis) and Intrepid (Rohm and Haas). This new chemistry is greatly needed. For example, if Bt cotton is not planted then Tracer is the only effective tool for tobacco budworm control. The pyrethroid class of chemistry, which gave effective budworm control for almost two decades, is no longer effective on budworms due to high levels of resistance. When growers have only one effective tool to suppress an economic insect, resistance is often the end result.

Following is a discussion of the number of generations or time of season when the major economic pests occur. In Alabama, these insects are seedling thrips, plant bugs, bollworms, tobacco budworms, aphids, fall armyworms and stink bugs.

Seedling Thrips:
Seedling thrips damage cotton from emergence to the eight to 10 true leaf stage. This pest is handled with either insecticide seed treatments or in-furrow applications at planting time on more than 80% of the planted acres. The remainder of the acreage would receive multiple foliar sprays at planting time. Under adverse growing conditions (cool, wet, dry) during the seedling stage, cotton may require foliar sprays if the at-planting treatments are not being taken up in the plants.

Plant Bugs:
Plant bugs historically were an economic problem in the early season between first square (fruit) and first bloom. However, due to the eradication of the boll weevil and the planting of Bt varieties, fewer foliar insecticides are required, leaving a much wider window for plant bug damage. Economic damage may now occur season-long, which has dictated new in-season scouting techniques and thresholds. Both phosphate and pyrethroid chemistry are effective on plant bugs. The first plant bugs enter cotton from wild hosts in May and June as cotton begins to fruit. Two or more generations may occur in cotton. In the latter part of the season, the population may shift primarily from the tarnished plant bug species to the clouded plant bug, which is more of a boll feeder.

Tobacco Budworms:
On conventional varieties, three generations of tobacco budworms may occur. The first occurs in June just as cotton begins to fruit. This generation is usually followed by a second in early July followed by others in August and September. Most growers either allow beneficial insects to control the first generation or use selective (soft) chemistry to aid beneficials in minimizing damage. Only one chemical, Tracer, has good activity on tobacco budworms. Tracer is expensive at $12 per acre application. From two to eight applications may be required per season, depending on the year and the location. For this reason, between 60% and 77% of Alabama’s cotton acreage over the past four seasons has been planted to Bt varieties.

Bollworms:
Bollworms reach damaging levels about peak bloom (mid July to early August) when they move in high numbers to cotton from maturing corn. They may occur at damaging levels at any time for the remainder of the season. The peak of their breakthroughs on Bt varieties corresponds to the peak movement from corn to cotton. On both Bt and conventional varieties, from one to four applications are necessary to hold bollworm damage below economic levels.

The pyrethroid chemistry remains very effective on the bollworm species. Pyrethroid applications targeted for bollworms also give suppression and/or control of plant bugs, stinkbugs and fall armyworms. On many acres, these applications are the first foliar insecticides applied during the season. Often, several damaging species have been present for several weeks at subeconomic levels. Significant yield increases have been documented in research tests from this clean-up of multiple pest species by one or two applications of pyrethroids.

Fall Armyworms:
In the southern part of the state, fall armyworms infest cotton at economic levels about the same time that bollworms move from corn. Two to three generations of fall armyworms may occur in the Gulf Coast area while economic levels from one or more generations may occur over all of south and central Alabama. Pyrethroids targeted for bollworms give 50% to 60% suppression of fall armyworms and have been the common choice of chemistry used. Under heavy fall armyworm pressure, tank mixtures with phosphates such as Curacron and Lorsban are used. The caterpillar complex in south and central Alabama is often a mixture of bollworms and fall armyworms from mid July to maturity (September) on Bt cotton. Conventional varieties would include these two species plus the tobacco budworm.

Aphids:
Aphids first appear in cotton at early fruit (June) and continue to build in numbers until about mid July at which time populations crash due to the naturally occurring fungus (Neozygites fresenii). With the exception of extreme drought conditions, most growers rely on the fungus to reduce populations. Aphids have developed resistance over the years to most available classes of chemistry. In Alabama, only imidacloprid (Provado) provides effective control at the current time. Aphids suck plant juices and excrete honeydew. Populations can be tolerated longer under good moisture conditions. Aphids interfere with scouting and the use of IPM thresholds for caterpillar pest due to the excessive secretion of honeydew and the clustering effect of thousands of aphids per plant. Scouts cannot effectively monitor these other pests under heavy aphid buildup. Aphids sometimes reoccur near the end of the season (late August) when cotton is maturing and the lower bolls are beginning to open. In this case, honeydew is secreted on the open lint causing a fungus (sooty mold) and sticky cotton, a condition that interferes with spinning when the cotton reaches the mills.

Stinkbugs:
Stinkbugs have been an economic pest since the boll weevil was eliminated. Applications to control weevils also controlled stinkbugs. Stinkbugs can be found in cotton season-long. However, since they are primarily boll feeders, they are only thought to be an economic insect from mid- to late-season (mid July to September) when developing bolls are present. Typically, one to three applications of either phosphates or pyrethroids are required. Due to a long life cycle (30-plus days), an application will give two or more weeks; suppression unless migration from other crops, such as corn, is occurring.

IPM and Cultural Practices:
Most other economic pests that occur on cotton in Alabama are sporadic in occurrence and can be detected by scouting and treated to minimize damage. Thresholds are established on these pests and cotton is monitored at least weekly for insects by private consultants, grower-employed scouts or agri-fieldmen. Four regional scout training schools are conducted annually by Extension entomologists. Total attendance at these schools is 400 to 500 persons annually. Most growers have attended a school on one or more occasions.

The timing of control measures is almost always based on field monitoring reports of one or more pests exceeding an economic threshold. Other than for the tobacco budworm on conventional varieties, the timing of an application is not of extreme importance. For best results, tobacco budworms must be controlled within 2 to 4 days after hatch. All other pests can wait for inclement weather, on irrigation schedules or until a grower’s ground equipment can reach a particular field. Boll weevil eradication and Bt varieties have moved growers back to primarily ground application of insecticides in Alabama. As a result, the aerial application business has suffered. Many have reduced the size of their operations, gone out of business or diversified into other types of application such as fertility, overseeding or forestry herbicide work.

More than 90% of the cotton acres in Alabama are monitored weekly and IPM thresholds are utilized. All other available IPM technology is utilized on the majority of farms due to the economic constraints of cotton production. IPM practices utilized include cultural practices (rotation, early planting, use of early maturing varieties, use of plant growth regulators, optimal fertilization, plant density), use of beneficial insects, selective chemistry, matching insecticides to proper target species, pheromone monitoring, species differentiation (Hel ID kits) and utilization of recommended insecticide rates. Other than genetically altered varieties for tobacco budworm control no other resistance varieties are available to growers. Cotton is grown in Alabama on row spacing that varies all the way from 7 inches (ultra narrow row) to 40 inches to skip row. However, row spacing has little or no impact on insect pests.

No organized resistance management programs are being conducted. However, growers are aware of the role of beneficials, using thresholds and alternating chemistry to minimize or reduce the development of resistance.

Biological Controls:
All growers utilize biological control programs if we interpret this to mean the use of naturally occurring parasites and predators. However, no artificially released organisms are utilized since they are not research proven, cost effective nor sustainable. Pheromones are utilized for monitoring but not for mating disruption. A series of eight to 10 pheromone trap locations are utilized for five of the key Lepidopterous species. Weekly reports are provided via e-mail, newsletter and 1-800-phone lines.

Other Issues:
No export or food processor restrictions are present that may limit the use of a given ingredient unless the European and antigenetically altered groups succeed in stopping or limiting the use of genetically altered cotton. If they do, the insecticide use on cotton will increase two- to fourfold over present day standards. This would effectively eliminate cotton as an economically viable crop in areas such as the coastal plains of the southeastern United Sstates (300,000 acres in Alabama) where Lepidopterous pest pressure is highest.

Ongoing research activities are underway to evaluate and find the appropriate fit for all new insecticide chemistry under development. However, economics play a vital role in replacement chemistry. In all instances, new replacement chemistry is more expensive and, therefore, is not suited for today’s cotton production climate. Furthermore, the EPA registration of new chemistries is unknown. There is no additional or more effective way to manage cotton insects in Alabama than the way it is being accomplished today. If a more effective way to manage cotton insects existed, it already would have been undertaken or implemented.

Table 2. Insecticide Usage Data: Data Presented in Four-Year Average, Beginning with the Introduction of Genetically Altered Varieties in 1996

Table 3. Insecticide Effectiveness Ratings
(Ratings range from 1 to 5, with 1 being Very Effective and 5 Not Effective.)

Table 4. Alternatives

Table 5. Yield Losses by Pest (1996-99)

Seedling Disease Complex
(Rhizoctonia solani, Pythium spp and Fusarium spp)

Seedling disease complex is a major problem on cotton in Alabama, involving multiple soilborne fungal pathogens including Pythium spp, Fusarium spp and Rhizoctonia solani. The effect of the complex includes pregermination decay of the seed, decay of the seedling on the way to the soil surface, partial or complete girdling of the emerged seedling at or near the soil surface and seedling root rot. Seed decay and pre- and post-emergence damping-off cause partial to nearly complete loss of stand. The effects of seedling root rot are often subtle, leading to a long-lasting weakness that reduces yield. Yield reduction to the seedling disease complex is estimated to be approximately 6% or about 42,015 bales a year.

These diseases are found in nearly all agricultural soils in Alabama. Incidence of these diseases is very dependent on weather conditions, particularly moisture. Cultural factors that delay seed germination or seedling growth enhance the possibility of severe disease problems. Such cultural practices include planting seeds too deeply or in soils that are excessively wet, cold, compacted, high in chemical concentrations or infested with nematodes or other pathogens.

Rhizoctonia solani exists as a large number of races that differ in their responses to various physiological factors, especially temperature and host. Continuous cropping to one host usually promotes an increase of that Rhizoctonia race on that crop. Growers often notice mounting losses from seedling diseases with continuous seeding to cotton. The fungus typically survives the winter as sclerotia (survival structures) in the soil. It can also live saprophytically on dead plant remains in the soil. The fungus can become parasitic when roots of a susceptible host penetrate the infested zone. Under certain conditions, filaments of the fungus penetrate the host epidermis and colonize soft tissues of the cotyledons, hypocotyls and roots of cotton seedlings. Infected tissue is often sunken and reddish brown in color. The fungus grows vigorously within the host, eventually transforming itself into dark-colored sclerotia. These structures can remain alive in the soil until susceptible host tissue reappear.

Pythium spp is also a soilborne fungal pathogen. A number of different Pythium species have been shown to be aggressive towards cotton. Pythium damage is greatest when post-planting soil temperatures are low and soil moisture is high. Symptoms caused by Pythium may vary. On hypocotyls, symptoms may range from small, discolored spots to large, necrotic areas. On severely damaged seedlings, the hypocotyls may be girdled by a soft, water soaked lesion or by a firmer, brown necrotic area. Affected seedlings die, either falling over or remaining upright during senescence.

Fusarium spp occur frequently in the microflaura community associated with cotton seedling diseases and are a major cause of seedling death. Several species of seed-borne and soil-inhabiting Fusarium have been identified in diseased seedlings. Fusarium spp usually invade seedlings stressed by extreme weather conditions, physical or chemical injury, or combinations of these factors. Symptoms usually include a reddish-brown to brown lesion on the stem at the soil line. The lesion may girdle the stem, killing the plant.

Alternatives/Cultural Control Practices: The incidence of cotton diseases can be reduced by the following practices:

• Destroy crop residue.
Plow cotton stalks under immediately after harvest to hasten decomposition. This practice reduces any potential seedling disease pathogens, nematodes and soil insect populations by depriving them of a place to overwinter.
• Rotate crops.
Rotation prevents the buildup of many disease-causing organisms in soil. If possible, plant cotton in a 3-year rotation rather than on the same land each year.
• Plant on well-prepared seedbeds and in well-drained soils.
Wet soils favor the growth of many soil fungi and retard the growth of cotton seedlings.
• Plant in warm soils.
Plant when the soil temperature at the 4-inch depth remains at least 68E F for three consecutive mornings.
• Lime acid soils.
Apply lime as recommended. Acid soils favor the development of seedling disease by restricting seedling growth and favoring the development of seedling disease-inciting fungi in the soil.
• Avoid chemical and mechanical injury.
Excessive rates of herbicides, fertilizers, insecticides or fungicides applied in the drill can injure seedlings, making them more susceptible to seedling diseases.
• Plant high-quality seed.
Poor-quality seed usually produces low vigor seedlings that are more susceptible to attack by fungi that cause seedling disease. Plant seed with a minimum 80% germination.
• Plant only treated seed.
Seed treatment will kill most fungal pathogens on the seed coat and protect the seed during germination.

Chemical Controls: A critical time to manage seedling disease complex is before planting. It is best to use only high-quality seed treated with a seed protectant fungicide. Seed should be planted only after soil temperatures average 68E F or above for several consecutive days. Seeding depth and rate will be dependent on seed quality and the expected weather conditions. An in-furrow fungicide also may be applied in areas with a history of severe seedling blight.

Table 6. Seedling Disease Complex: Chemical Controls for Cotton Production

Fusarium Wilt

Fusarium wilt symptoms can appear at any stage of plant development, but they vary with environmental conditions and the degree of resistance of the host. Fusarium wilt is caused by the fungus Fusarium oxysporum. A number of physiological races of F. oxysporumexist, distinguished by the reactions of differential hosts. The organism survives for long periods of time in soil and on cotton debris or other organic matter in the soil. It may enter the cotton roots through wounds or through the cuticle. Once the fungus invades the vascular system, disease occurs.

Although Fusarium wilt can occur in cotton in the absence of nematodes, nematode feeding increases the susceptibility of plants. When both pathogens are present, a synergistic reaction occurs, potentially increasing damage to the plant. Root-knot nematodes appear to cause the greatest increase in Fusarium wilt incidence.

Control: Control consists of avoiding fields with a history of Fusarium wilt and planting Fusarium wilt-resistant cultivars. Controlling nematodes will also reduce incidence of Fusarium wilt.

Boll Rots

Boll rots cause losses in all cotton growing regions of the world. Damage is more common in areas with high rainfall. Losses due to boll rots have been recorded as high as 50% in some locations. In Alabama, losses to boll rots are estimated to be approximately 4% a year or approximately 28,000 bales of cotton.

Approximately 170 species of microorganisms, many of these fungi, have been implicated as causes of boll rot. Some of the more common fungal organisms known to cause boll rot include Diplodia gossypina, Ascochyta gossypii, Glomerella gossypii, Fusarium spp, Pythium spp and Rhizoctonia solani.

Diplodia infections eventually cause the bolls to turn black. Thereafter, the boll dries rapidly and often splits open, exposing the blackened remnants of fiber and seed. With Glomerella boll rot as much as 50% of the boll may be consumed by decay. The lint within, a blackened mass, is difficult to remove from the imperfectly opened boll. Fusarium boll rot results in a blue-black to brown rot of the boll.

The life cycle of most boll rots appears to fall into one of three general groups: soilborne organisms, seed-borne organisms and organisms that live above ground as foliar pathogens or as saprophytes. In all three types, prolonged periods of high humidity or free water on the surface of the boll are essential for boll infection, but not for the subsequent decay of bolls.

Control: General control practices include planting high-quality, disease-free seed treated with a fungicide and using resistant varieties. Most control measures are targeted at preventing excessive plant growth to provide more sunlight penetration and decrease the relative humidity within the canopy. Control practices that address this would be restraint in the use of nitrogen fertilizer and dense stand plantings. Effective control of insect damage to bolls also reduces this disease. Chemical controls are typically not recommended for boll rot control.

Plant-parasitic nematodes are a serious threat to cotton production in Alabama. Nematodes spend their entire lives in the soil, feeding on cotton roots. Aboveground symptoms of nematode injury include stunting, poor fruit set and signs of potassium deficiency. The severity of nematode injury is determined by the species present and their population level.

Nematodes typically spread from field to field by means of nematode-infested soil particles or clumps clinging to cottonseed, farm equipment or the soles of workers’ shoes. Once in a field, nematodes are spread by cultivation. Once nematodes become established in a field, they remain there forever.

Reniform nematodes (Rotylenchus reniformis) and root-knot nematodes (Meloidogyne incognita) are responsible for 99% of the nematode damage in Alabama. Reniform nematodes are the most damaging nematode pests on cotton. It is estimated that reniform nematodes cause a 7.5% yield loss in cotton production or approximately 52,000 bales of cotton in Alabama.

Reniform nematodes begin feeding on the roots of young cotton plants. The adult female is the only stage that feeds. The young female enters the cotton root and begins to feed as a semiendoparasite. The female will lay from 40 to 70 eggs. The reniform nematode completes its life cycle in 21 to 35 days at soil temperatures between 77E F and 86E F. It is estimated that reniform nematodes produce up to seven generations in the southern part of the state and as many as five in the northern part of the state. Reniform nematodes have a wide host range that includes soybean, tobacco, vegetables, winter legumes and many weeds. Reniform nematodes do not reproduce well on many grain crops.

Cotton root-knot nematodes rank second to reniform nematodes in importance in Alabama. It is estimated that root-knot nematodes cause about a 0.5% loss in yield annually or about 4,000 bales of cotton in Alabama. Root-knot nematodes complete their life cycle in about 30 days at 80E F. Root-knot nematodes are considered sedentary endoparasites. Females lay from 300 to 1,000 eggs. The host range of the cotton root-knot nematode also includes soybean, corn, many vegetables and many winter grass-type cover crops. Many weeds also can act as hosts to this nematode.

Nematode Management: Nematodes can be managed in cotton through the use of crop rotation, resistant varieties, certain cultural practices and nematicides.

• Crop rotation:
  Crop rotation is effective in controlling both reniform and root-knot nematodes where profitable alternative nonhost crops are available. Peanut and grain sorghum are examples of alternative nonhost crops. Corn and soybean varieties with resistance to the cotton root-knot nematode are other alternatives in a crop rotation system.
• Fallowing:
  Fallowing nematode-infested fields is another way to control reniform and root-knot nematodes. Weed control in the target field is essential for fallowing to be effective. No commercial cotton varieties have resistance to reniform nematode or cotton root-knot nematode. However, some varieties do have various degrees of tolerance to root-knot nematodes.
• Cultural practices: Cultural practices can be used to prevent spread of nematodes from one field to another. Nematode-infested fields should always be worked last if possible and farm equipment should be washed before entering clean fields. Nematode populations can be reduced by fall cultivation. Turning the soil and exposing the roots subjects the nematodes to the heat and drying action of the sun.

Nematicides are currently the most effective tool for controlling reniform nematodes in cotton. Nematicides have been shown to increase cotton yields from 40% to 75% in heavily infested fields. Though relatively expensive, nematicides are ideal where rotation is not feasible. Nematicides provide protection for the first 4 to 6 weeks of the season, which is enough time for the plant’s root system to develop.

Chemical Control (Nematicides): Approximately 35.9% of the cotton acreage in Alabama received fumigants or nematicides to control nematodes in 1997. (8)

Table 7. Nematode Chemical Controls for Cotton Production

Timing

All the cotton acreage in Alabama is infested with one or more species of weeds. Weeds are estimated to cost cotton producers in the state about 8% of their potential yield, even with the current weed control technology available (11). More than 20 weed species are of economic importance in Alabama cotton fields. Sicklepod, annual morningglory, prickly sida, large crabgrass and other annual grasses, pigweed, nutsedge and common cocklebur are the most common and require herbicide treatments each year to provide control. Other weeds such as bermudagrass, wild poinsettia, horsenettle and tropic croton are less common, but require specialized treatments to reduce their competition and spread. Weeds of regional importance in Alabama include redweed in south Alabama, Florida beggarweed, bristly starbur and Texas panicum in southeast Alabama and velvetleaf in north Alabama.

Cultural Practices:
Cultural practices are changing as the herbicides available for weed management in cotton change. Currently, the cotton acreage in Alabama is dominated by Roundup Ready varieties, which allow the use of Roundup Ultra herbicide to be sprayed over-the-top for control of emerged weeds. Roundup Ultra is a broad spectrum postemergence herbicide that has no soil-residual activity. This genetic technology has been widely adopted by cotton growers across the state and the Southeast and puts significant pressure on the biological system to select for weeds that Roundup Ultra herbicide will not control. Roundup Ready soybeans and corn are also being used in Alabama. This is rapidly shifting weed management to dependency on a one-product system. No-till acreage is increasing across Alabama due to the availability of postemergence herbicides that can be used in all row crops. The weed spectrum in no-till fields will probably be different than the spectrum in conventional tillage fields. An increase has been seen in the perennial species in no-till cropping, weeds that are often harder to control than are annuals. Older soil-residual herbicides, such as norflurazon and flumeturon, are being used less and less in cotton fields across Alabama. This may seem to be beneficial to the environment overall; however, these herbicides have never posed a problem to our environment when used in a manner consistent with the label instructions. Because of intense economic pressure applied from exclusive usage of genetically modified crops, some of these older products may no longer be used. If weed resistance problems develop in the near future due to overuse of one product, then the availability of the older products with their different modes of action would be invaluable for dealing with this situation.

BXN Cotton:
BXN cotton varieties that allow the application of Buctril herbicide over-the-top are currently available, but most growers in Alabama are not using this genetically modified variety because Buctril will not control sicklepod or grass species. Staple herbicide was registered for use in 1996 and has been widely used by cotton growers since that time due to its postemergence and preemergence activity on broadleaf weeds and the fact that it can be used on all varieties. Staple use has also declined recently due to the widespread adoption of Roundup Ready technology. Staple can be mixed with Roundup and used postemergence on Roundup Ready cotton varieties. This treatment will probably be used more in the future due to the increased activity of the mixture on annual morningglory species that Roundup is sometimes weak on. Staple herbicide belongs to a herbicide family (classed as an ALS inhibitor) for which weed resistance has been well docu