Crop Profile for Corn in North Carolina

Prepared: January, 1999
Revised: November 1999

• North Carolina ranks 16th in U.S. production of field corn, 9th in sweet corn.
• North Carolina produces 1 percent of the total U.S. field corn crop and 3 percent of the sweet corn.
• North Carolina produces an unknown but small amount of popcorn and yellow and white field corn for milling purposes and an unknown but very small percentage of the popcorn and milling quality field corn.
• In 1997, 77,430,000 bushels of field corn grain valued at $228,419,000 were produced on 870,000 acres.
• The same year, 1,050,000 tons of field corn silage valued at $10,500,000 were produced on 75,000 acres.
• Again in 1997, sweet corn valued at $9,653,000 was produced on 6,500 acres.
• Production costs for field corn average $227.93 per acre.
• Production costs for sweet corn are estimated at $1,086 per acre.

Production Regions

Corn is grown throughout North Carolina, including the mountain counties. Major acreage of grain corn is grown in the coastal plain and tidewater regions with some grain produced in the piedmont. Most silage corn acreage is in the piedmont and is associated with livestock production (e.g., dairy). Sweet corn is produced mainly in the coastal plain.

Production Practices

The vast majority of corn is grown under non-irrigated conditions (rain-fed); sweet corn is more typically irrigated. Corn is grown on a wide variety of soil types from loamy sands to clays to organic soils. Conventional, strip-tillage, and no-tillage cultures are all widely practiced. Recently, there has been a shift to conservation tillage (no-till, strip-till, minimum-till), and this trend continues today. Typically, corn grown in the coastal plain is rotated, whereas it usually is not in the piedmont or mountains. Field corn is characterized by early inputs of fertilizer, herbicide, and insecticide followed by little attention until harvest. Field corn culture, including harvest and postharvest handling, is totally mechanized. Sweet corn culture is similar to field corn except for intensive use of insecticides (during the reproductive period), irrigation, and manual labor.

Use of insecticides and loss of phosphate and carbamate insecticides:
The vast majority of field corn and sorghum gets less than a single application of insecticide yearly. Both crops have a low profit margin, and growers are reluctant to spend money on insecticides, except where there is a demonstrated or perceived risk. Many of the insects listed below, with accompanying phosphate or carbamate insecticide, are very sporadic in distribution, both in time and space. Whereas the pest may not be of much value within a single year, there are some years when the pest can be very important. Likewise, a pest may not occur over much of the production area but may be very important on specific farms.

Flexibility is very important in meeting pest management needs appropriately. Having a variety of products is critical to managing pests and allowing sustainability in the agricultural system. Insect resistance also places high demand on having insecticidal compounds that can serve as alternatives or mix components. Losing pesticides through market attrition, pest resistance, and regulatory restriction can leave the pest manager and grower in an inferior position. For example, North Carolina has the second largest contiguous area of organic soils in the U.S. Much of this acreage is devoted to corn production. Currently, only two insecticides, terbufos and carbofuran, remain viable alternatives for billbug and wireworm control. Both have had the use-rates reduced, although one has had former rates reinstated via a special state label. Both are potential candidates for cancellation. The loss of one or both products will seriously affect corn insect management and farm sustainability in the region.

Corn is attacked by a wide variety of insect pests, about 25 species. All stages of the crop and all plant parts are attacked by one or more insects. The crop is most susceptible in the seedling stage, and management efforts involving insecticides are most often directed to this stage in field corn. The early whorl stage is also attacked. Ear-feeding insects are a severe problem in sweet corn due to the low tolerance of insects by the marketplace. Sweet corn is intensely treated with insecticide in the reproductive stage. Cultural practices enhancing insect pest levels include planting late, conservation tillage, and restricting rotation. The most commonly encountered insect pests include corn wireworm, southern corn billbug, western corn rootworm (in the piedmont and mountains), black cutworm, fall armyworm, European corn borer, corn earworm, and southern cornstalk borer. Insect pests that are infrequently encountered at economically damaging levels include armyworm, brown stink bug, cereal leaf beetle, corn leaf aphid, corn root aphid, grasshopper, green bug, Japanese beetle, maize billbug, northern corn rootworm, seedcorn beetle, sod webworm, southern corn rootworm, stalk borer, sugarcane beetle, and white grubs.

Sorghum is attacked by many of the same insect pests that infest corn, but there are a few exceptions (e.g., sorghum midge and sorghum webworm). Also, since sorghum is often planted late, it is subject to injury by late-season caterpillars, notably the fall armyworm, corn earworm, and European corn borer.

Wireworms

Crop interactions:
Two or more wireworm species infest corn, with Melanotus communis being the most important. Wireworms have an erratic distribution in time and space. The larvae eat the germinating seed as well as the seedling. When populations are high, wireworm feeding can severely reduce seedling stands and significantly reduce yield. These insects sometimes have multi-year life cycles, and their associations with other crops and weeds are not well understood. Wireworms are very difficult to predict or monitor (they are within the soil and cannot be readily observed); therefore, insecticide-use decisions tend to be based on history of infestations, tillage type, soil type, certain rotation patterns, and other associated factors that lead to increased risk.

Control:
A preventative insecticide treatment of a granular or in-furrow liquid spray formulation is commonly used at planting time in areas where wireworms are perceived to be a significant risk. A single application is used on both field and sweet corn. Terbufos, chlorpyrifos, phorate, or liquid carbofuran are most commonly used. Some tefluthrin and Aztec are used. Reduced tillage corn and corn planted to set-aside land tend to have greater wireworm infestations. In conventional tillage, most serious wireworm infestations are in corn rotated with soybeans. There are no cultural control methods directed specifically to wireworm management. There is no treatment for wireworms that can be applied after planting. On organic soils, only terbufos and carbofuran are used, as others are not effective on these soil types.

* May include other pest insects

Billbugs

Crop interactions:
Two species of billbugs infest North Carolina corn: the southern corn billbug, Sphenophorus callosus, and the maize billbug, S. maidis; there are other species of minor importance to corn. The southern corn billbug is the most common species. Billbug adults feed on seedling corn and lay eggs into the stalks. Larvae develop within the root crown. If billbug numbers are high, they can severely damage the corn crop, especially when weather or other conditions inhibit the growth of seedlings.

The insects have a one-year life cycle, have few alternate hosts, and move primarily by crawling. Consequently, rotation can be very influential unless alternate hosts are available, primarily nutsedges. Billbugs are most common in the tidewater areas and in cleared lowlands across the coastal plain. However, they can become significant pests almost anywhere if ecological situations favor their development and survival.

Control:
An integrated approach is essential to successful billbug management in most areas of the coastal plain. The strategy includes rotation, promotion of rapid seedling development, early planting, at-planting insecticide use, scouting, and postemergence insecticides. At-planting and postemergence insecticides include terbufos, chlorpyrifos, and carbofuran. These are the only effective insecticides (of any class) currently registered for these purposes. On organic soils, where much of the billbug problem occurs, chlorpyrifos is not effective (due to organic matter tie-up). Also, liquid carbofuran is not labeled at a high enough rate to be effective as an at-planting treatment for billbugs.

Insecticides are used to cut adult billbug numbers, thereby reducing current year crop injury as well as limiting the population the following year. If billbugs are allowed to build up, crop loss and insecticide use dramatically increase. Successful billbug management relies completely on an integrated use of cultural controls and insecticides, as neither approach is adequate alone.

* May include other pest insects

Corn rootworms

Crop interactions:
The rootworm complex consists of three species: western corn rootworm, Diabrotica vergifera; southern corn rootworm, D. undecimpunctata howardi; and northern corn rootworm, D. barberi. Western and northern corn rootworms are similar in habit, overwintering as eggs in last year’s corn fields and having one generation a year. Southern corn rootworm overwinters as an adult and has two to three generations per season. Western and northern corn rootworms occur in the mountains and piedmont, but are migrating east, whereas southern corn rootworm is distributed throughout North Carolina. The most important species of the complex is the western corn rootworm. Larvae hatch and feed on seedling to whorl stage corn, eating the roots. Damaged plants are less thrifty and often blow over. Southern corn rootworm also attacks seedlings, feeding into the meristem and killing the plant. Under high populations rootworms can seriously reduce the yield of corn (grain or silage). The incidence of western corn rootworm has greatly increased in the last decade in western North Carolina, and it has been found well into the coastal plain.

Control:
Rotation is very effective against western and northern corn rootworms but not the southern. However, farmers in the western half of the state have limited opportunity to rotate and thus use at-planting insecticide to reduce rootworms. Phosphate insecticides used against rootworms include terbufos, phorate, and chlorpyrifos. The carbamate insecticide carbofuran is used to a minor extent. Other insecticides include tefluthrin and Aztec.

In the last five years insecticide use for management of these pests has greatly increased and is predicted to climb further. In the eastern corn-growing areas, early generation southern corn rootworms are fortuitously controlled by at-planting insecticide used against wireworms and/or billbugs.

* Currently, rootworms are restricted to the western part of North Carolina, where a minor portion of the corn crop is grown. May include other pest insects.

Black cutworms

Crop interactions:
Black cutworm, Agrotis ipsilon, is a sporadic pest of many crops, including all types of corn. This insect is a threat to the seedling stage of the crop. Cultural conditions which favor early weed growth, poor crop growth, and plant residue on the soil surface (e.g., conservation tillage) are favorable to increased black cutworm problems. Typically, when the corn crop is planted, the caterpillars are in the field as eggs, which are deposited in late winter or very early spring. Young caterpillars eat foliage, and larger stages cut the plants off and drag the seedling top into the soil where they eat it. On soft soil, like organic soils, the black cutworm may be mostly subterranean in habit. Plants that are cut off soon after emergence will recover, but plants cut after the three-leaf stage die. When populations are high, this insect can destroy a crop, often forcing replanting.

Control:
In North Carolina black cutworm is primarily managed through scouting, use of thresholds, and applying foliar insecticide as needed. In some instances, at-planting insecticides (e.g., chlorpyrifos, Aztec) used for wireworms, rootworms, or other soil insects also have activity against moderate infestations of cutworms. In other instances, where a history of chronic cutworm problems exist and corn is grown without tillage, the grower may add an insecticide (usually a pyrethroid) to the burn-down herbicide mixture. Only a small percentage of the overall corn acreage is treated for cutworm.

* Used for a complex of insects including wireworm and billbug

Corn earworms

Ecology and crop interactions:
The corn earworm, Helicoverpa zea, is a major insect in corn. It may infest whorl leaves, tassels, and the ear. Wherever corn is grown in the southern U.S. and up the mid-Atlantic states, the corn earworm uses the crop as a nursery. Ear stage corn is an almost ideal habitat, and high numbers are reared in this crop that later move to other crops (e.g., cotton, peanuts, soybeans, vegetables) for colonization, causing the primary insect problem in these crops. Corn earworm feeds on the distal end of corn ears, causing direct damage; it is also implicated in mycotoxin contamination of the grain. Sweet corn ears that contain a caterpillar or damage are considered unmarketable. In sweet corn, corn earworm is the primary damaging pest of a complex of three ear-infesting caterpillars (corn earworm, European corn borer, and fall armyworm).

Control:
Early planting helps to avoid heavy corn earworm infestation in most circumstances. However, in field corn it is not possible economically to control corn earworm with any technique, including insecticide. Farmers growing field corn accept yield reduction and contamination due to the insect. In sweet corn, though, extensive use of insecticide is required to produce insect-free ears that are acceptable to the market. Phosphate, carbamate, and pyrethroid insecticides are heavily used to control ear-feeding caterpillars, of which corn earworm is the primary pest. The recent introduction of ear-expressing transgenic Bacillus thuringiensis (Bt) field corn shows promise for managing corn earworms in this crop. However, there are concerns about cross resistance arising in corn earworms to Bt corn and Bt cotton.

* May be included as a tank-mix partner or alternating insecticide within the total scheduled ear-protection spray program for one or more applications to sweet corn.

Fall armyworm

Ecology and crop interactions:
Fall armyworm, Spodoptera frugiperda, does not overwinter in North Carolina. It migrates into the state from the south and arrives in May. As the growing season progresses, fall armyworms become increasingly abundant. This insect favors corn but infests many crops. However, it is not considered a significant pest in field corn, which is usually planted early in the season (mainly March and April). By the time fall armyworms become abundant, field corn has matured and is unattractive to egg-laying moths. However, it can be a significant pest of late-planted corn (e.g., silage corn). Infestation begins in the whorl but may progress to the ear and stalk. It can be very damaging.

In sweet corn, the insect pest infests ears and makes them unmarketable. It is one of the ear-infesting complex in sweet corn (fall armyworm, corn earworm, and European corn borer).

Control:
Early planting and using field corn hybrids that mature within 120 days are the major tactics growers employ against fall armyworms. In late-planted field corn, scouting, thresholds, and insecticides are used to manage problem infestations. These infestations are uncommon. Recommended insecticides include a carbamate, a phosphate, and a pyrethroid. In sweet corn, insecticide applications designed to control ear-feeding caterpillars target fall armyworms.

* On field corn.
** Used on field and sweet corn for whorl treatment; may be included as a tank-mix partner or alternating insecticide within the total scheduled ear-protection spray program for one or more applications to sweet corn.

European corn borer

Crop interactions:
European corn borer, Ostrinia nubilalis, is a common insect pest of several North Carolina crops. It can sustain up to three yearly generations, of which two normally develop on field corn (either first and second generations on early-planted corn or second and third generations on late-planted corn). Larvae infest the whorl, stalks, and ears. Infestation can result in physiological disruption and stalk breakage. Yield loss in field corn can be as high as 50 percent. In sweet corn, European corn borer is one of the ear-infesting insects (European corn borer, corn earworm, and fall armyworm) that can greatly affect marketability of the product.

Control:
Management of European corn borer is presently based on cultural techniques that focus on maturing the crop early to avoid high, late-season populations. These techniques do not affect first- and second-generation corn borers. An insecticide program that includes pheromone trapping, sequential scouting, application of thresholds, and insecticide application is available. However, the high variation of damaging infestations across time and space makes the program only marginally cost effective. Consequently, growers do not rely on this approach. There is a desire to use transgenic Bt field corn against this pest. In sweet corn, European corn borer is intensively managed with insecticide as part of the overall effort to control ear-feeding caterpillars.

*Minor % for field corn.
** May be included as a tank-mix partner or alternating insecticide within the total scheduled ear-protection spray program for one or more applications to sweet corn.

Sap beetles

Crop interactions:
Larvae of the sap beetle (picnic beetle), Nitidulidae, infest the ears of corn and puncture kernels. Often they are associated with injury caused by other ear-feeding insects, but this relationship is not essential for infestation. They are not considered a problem in field corn, although their presence may be associated with increased mycotoxin contamination. However, in sweet corn, sap beetle-contaminated ears and damaged kernels affect marketability.

Control:
Sap beetles are not managed in field corn. In sweet corn they are ordinarily controlled by the insecticide applied for ear-feeding caterpillars. In some circumstances a beetle-specific insecticide may be used as a tank-mix partner with caterpillar-active insecticide to help keep sap beetles from infesting sweet corn ears.

* May be included as a tank-mix partner within the total scheduled ear-protection spray program for one or more applications in sweet corn.

Brown stink bugs

Crop interactions:
The brown stink bug, Euschistus servus, attacks grass crops. In corn, it can feed on and reproduce on all above-ground plant parts throughout the season. Until the advent of no-tillage corn, the brown stink bug was considered only a minor pest, not justifying management expense. However, it appears that the bug overwinters in crop residues preceding the planting of no-tillage corn. The brown stink bug has become a greater pest as acreage of no-tillage corn has increased. Corn seedlings and adult bugs become active in concert, and the bugs feed at the plant meristem. Feeding can cause plant death and deformation. When bug numbers are high, very serious crop damage can ensue.

Control:
Scouting, thresholds, and insecticide application are the only tactics that work against brown stink bugs. At-planting insecticides used for soil-dwelling insect pests and billbugs have little effect on stink bugs.

Sod webworms

Crop interactions:
Sod webworms and other webworms, Crambus sp., are limited, as pests, to no-tillage corn culture. The caterpillars attack plants in the early seedling stage and can defoliate corn and eat the meristem, causing plants to die. Webworm damage declines rapidly after plants reach the 6- to 8-leaf stage. They are very minor pests.

Control:
Scouting, thresholds, and insecticide application are the primary tactics used against webworms. At-planting insecticides used for soil-dwelling insects and billbugs have little effect on webworms. If populations are adequately high, a remedial insecticide is often recommended. Phosphate and carbamate insecticides are not used against webworms in North Carolina. A pyrethroid insecticide is recommended.

Aphids

Crop interactions:
Several species of aphids attack corn, mainly corn leaf aphid, Ropalosiphum maidis, and greenbug, Schizaphis graminum. They are minor pests.

However, greenbug has become more significant with the growth of no-tillage corn culture. Early greenbug infestations develop on bluegrass, a winter grass, and move to corn seedlings after the bluegrass is herbicide-killed. Greenbugs inject a phytotoxin that kills or stunts corn seedlings. Corn leaf aphids can become a problem on sweet corn.

Control:
Scouting, thresholds, and insecticide application are the primary tactics used against aphids. At-planting insecticides used for soil-dwelling insect pests and billbugs can reduce aphid populations.

* Does not include systemic soil-applied insecticide used for wireworm, billbug, or other pests which fortuitously control aphids.

Grasshoppers

Crop Interactions:
Grasshoppers (several species) frequently inhabit corn fields, but they are very minor pests in North Carolina. They can be a significant local problem, especially in seasons following a dry year and especially where conservation tillage is practiced. Small grasshoppers can defoliate corn seedlings. Later in the season, high numbers of large grasshoppers invade fields from the edges where they developed. Defoliation of plants along the edges of fields can be significant. Whole fields are usually not defoliated unless they are small.

Control:
Insecticide is usually applied to defoliating populations of grasshoppers. Application is usually confined to fields with significant interfaces and to "spot spraying" field edges.

Chinch bugs

Crop interactions:
Chinch bug, Blissus leucopterus leucopterus, infestations are limited to organic soil areas in the tidewater region and to cleared pocosins. They are very minor pests. Bugs attack corn in the seedling stage and suck sap from the plants. Plants can be stressed and suffer abnormal growth.

Control:
Chinch bugs are usually fortuitously controlled by the at-planting systemic insecticide used for wireworms and billbugs (phosphate and carbamate insecticides). If high populations occur on seedlings, a foliar insecticide may be used.

Armyworms

Crop interactions:
Armyworms, Pseudaletia unipunctae, are occasionally found in grassy or no-tillage corn where grasses are abundant. Moths will not lay eggs on corn but will infest many species of wild grasses. In conventional corn, poor grass control may lead to caterpillars that eat the grass and move to corn plants to feed. In no-tillage corn, the caterpillars are present before planting. After the grasses are herbicide-killed and corn seedlings emerge, caterpillars move to the seedlings to feed. If caterpillar numbers are high, damage can be severe.

Control:
Armyworms are an infrequent problem. Therefore, growers are encouraged to scout their fields. If damaging populations are found, an insecticide is recommended.

North Carolina Integrated Pest Management

North Carolina Pesticide Impact Assessment Program

Scouting Corn in North Carolina

Scouting for Corn Insects

Insect Pests of Corn

Major Corn Diseases in North Carolina

Pesticides & Wildlife - Corn

Grain Market News

Corn and other Summer Vegetables, Horticultural Commodity of North Carolina

John Van Duyn, Extension specialist, V. G. James Research and Extension Center,
North Carolina State University

Ronnie Heiniger, Extension specialist, Department of Crop Science, North Carolina State University

1. Crop Protection Reference. C&P Press. New York, N.Y.
2. 1998 North Carolina agricultural chemicals manual. North Carolina State University. Raleigh, N.C.
3. North Carolina Department of Agriculture and Consumer Services Statistical Services. Raleigh, N.C.