Early Season Corn Insects

  • Early season corn insects feed on corn seeds and seedlings and can cause delayed emergence, stand loss, plant injury, and stunting.
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  • Regular scouting is necessary to determine if insect populations have reached the action threshold, which usually warrants treatment.
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  • Management options can include cultural practices, seed treatments, and insecticides.
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Be on the Lookout this Spring

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Scouting for early season insects should occur when examining fields for seedling emergence and corn stands this spring. Early season insects that feed on corn seeds and seedlings can cause plant injury, stunting, delayed emergence, or stand loss.

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Types of Early Season Corn Insects

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Figure 1. Seedcorn maggot larvae damage.
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Seedcorn maggots (Delia platura) are yellowish-white, about 1/4 inch long, and lack defined heads and legs. Seedcorn maggot larvae can reduce stands by burrowing into seeds and feeding on kernels before germination (Figure 1). Fields that are high in residue or manure are more susceptible to seedcorn maggot damage.

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Figure 2. White grubs.
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White grubs (Phyllophaga spp.) are the larval stage of May and June beetles. They can be distinguished from other grubs by the zipper-like spines under the abdomen (Figure 2). White grubs feed on plant roots, which can cause plant wilting. Small plants may be killed and larger plants may be stunted.

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Figure 3. Wireworm larva.
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Wireworm (Agriotes, Limouius, etc. spp.) larvae are slender, hard-bodied, and brownish in color. They are about 1 inch long when fully grown and feed on seeds and seedlings below ground (Figure 3). Gaps or wilted plants within the row may indicate the presence of wireworms.

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Figure 4. Black cutworm larva and clipped corn seedling.
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Black cutworm (Agrotis ipsilon) larvae appear greasy and vary in color from light-gray to black with a length of about 1 1/2 inches long. Larvae are nocturnal and will curl up if disturbed (Figure 4). Larval feeding can occur at the base of corn plants or underground, which results in wilted or completely clipped seedlings.

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Figure 5. Chinch bug adult.
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Chinch bugs are small, roughly 1/6 inch in length, with a black body and white forewings that create a white 'X' on the abdomen (Figure 5). Newly-hatched nymphs are bright red. Chinch bugs feed on the crowns and stems of corn plants and below ground on roots. Feeding damage from adults and nymphs causes reddish discoloration of leaves and stems.

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Figure 6. Japanese beetle larvae.
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Photo courtesy of John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org.
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Japanese beetle (Popillia japonica) larvae are white grubs with distinct dark-brown to orange head capsules (Figure 6). Larvae grow from about 1/16 inch long to about 1 1/4 inches long when mature. Larvae feed on plant roots, and mature beetles can continue to cause damage throughout the season.1

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Management Approaches

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There are several management practices that can help reduce early season corn insect damage. Crop rotation with a non-grass crop, conventional tillage, and timely planting in good soil conditions can help reduce corn seedling stress and align timing of corn insect susceptibility with lower insect pressure.

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Insecticide rescue treatments are available for some insects; however, timing is critical, which makes preventative treatments beneficial and necessary for some insect species. Insecticidal seed treatments can help to control several early season insects for up to 30 days after planting. Insecticide seed treatment products, such as clothianidin, can help reduce damage caused by secondary pests including: seedcorn maggot, white grub, wireworm, black cutworm, Japanese beetle larva, and chinch bug. Chinch bug control may require a higher rate of clothianidin. Fields should be scouted regularly, and pest identification and population recorded. Treatment action thresholds (Table 1) can vary by state, pest, and stage of crop development. Contact an Extension entomologist and/or agronomist for local recommendations. If a threshold is met, apply the appropriate insecticide promptly and according to label requirements.

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Table 1. General treatment recommendations and action thresholds for early season corn insects.
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 Early season corn insects
Treatment options and action thresholds 
 Black cutworm
 Preventative treatment or rescue treatment when 2 to 4% of the plants are cut belowground or 6 to 8% of the plants are cut above the soil surface and cutworms less than 1 inch long are present.2
 Wireworm
 Preventative treatment or 1 or more wireworms per bait station.3
 True white grub
 Preventative treatment or before planting, use direct soil sampling method. One white grub per square foot is enough to cause significant stand loss.4
 Seedcorn maggot
 Preventative treatment or replanting only.5
 Chinch bugs
 Treat after damage begins.6
 Japanese beetle larvae
 Currently, thresholds exist only for adult feeding during tasseling.7
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Sampling for Early Season Corn Insects

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Soil sampling can be used to determine the presence of white grubs and Japanese beetle larvae. Examine a 1-foot by 2-foot by 6-inch deep volume of soil and count the number of grubs per sample. Take one soil sample for every 1 to 2 acres a few days prior to planting.

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Bait stations for wireworm sampling consist of approximately 1/2 cup each untreated wheat and corn seeds placed 4 to 5 inches deep in the soil. A piece of black plastic covered by a larger piece of clear plastic can be placed on the soil surface above the trap to increase soil temperature and facilitate germination. Traps should be installed 2 to 3 weeks prior to planting and placed uniformly throughout the field.

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Baited wire traps can be used to sample many of the below ground corn insects including: wireworms, white grubs, Japanese beetle larvae, and seedcorn maggots. Traps consist of 20 untreated corn seeds spaced evenly along a 2-foot long by 3-inch wide strip of wire mesh in 2-inch deep furrows and covered with soil. Wire mesh should be bent lengthwise at a 90° angle to keep seeds in place. Traps should be installed 2 to 3 weeks prior to planting and placed uniformly throughout the field at approximately 1 to 2 traps per acre.

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Scout for black cutworms 1 to 2 times a week beginning with plant emergence. Observe plants throughout the field for evidence of leaf feeding or cutting.

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Scout for seedcorn maggots after planting by sampling the soil in areas where plants have failed to emerge. In these areas, dig up 2 feet of row in each of 5 areas of the field and examine ungerminated seeds for damage and the presence of maggots.

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Sample for chinch bugs by examining leaves and roots of 20 plants in border rows for the presence of adults and nymphs.

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