Early Season Corn and Soybean Insect Pests

Throughout the year, different insect pests pose potential threats to crop health and yield potential. Knowledge of when and where to look for particular pests is an important part of the scouting process
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Early Season Insect Pests. Cool, moist soil conditions favor the development of many soil insects. These conditions can also slow corn and soybean growth allowing soil insects a longer time to feed on tender plant tissue.
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CORN AND SOYBEAN INSECTS

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Seedcorn maggot (Delia platura) can be a problem of corn and soybean in soils that are high in organic matter (manure, clovers, etc.) as the adult flies are attracted to the material to lay eggs. The yellowish white maggot is about ¼-inch long when mature (Figure 3). Maggots burrow into the seed, often destroying the seed’s ability to germinate. The seeds fail to germinate and plants do not emerge leaving large gaps in the stand. Unlike wireworm damage, maggot damage usually covers most of a field.
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Figure 1

Figure 3. (top left) Yellowish-white seed corn maggot larvae. Photo courtesy of Whitney Cranshaw, Colorado State University. Bugwood.org. (top right) Seedcorn beetle. Photo courtesy of Kansas Department of Agriculture Archive, Bugwood.org(bottom left) Wireworm. (bottom right) Gray garden slug. Photo courtesy of Joseph Berger, Bugwood.org

13;10;Slugs. Several species of slugs can be pests of corn and soybean; however, the gray garden slug (Deroceras reticulatum) is the species of slug that most commonly causes damage. Slugs cause the most damage during crop establishment and early growth. Damage is most severe under cool and wet conditions. Slugs feed at night and hide in residue or soil during the day. Slugs are legless, soft-bodied, slimy, white, gray, or black gastropods (Figure 3). In corn, slugs scrape small strips in the leaf, leading first to window-pane damage and then leaf-shredding. In soybean, slugs create craters in the cotyledons and then ragged holes in the leaves. Slime trails are often seen in close association with their damage.
Slugs. Several species of slugs can be pests of corn and soybean; however, the gray garden slug (Deroceras reticulatum) is the species of slug that most commonly causes damage. Slugs cause the most damage during crop establishment and early growth. Damage is most severe under cool and wet conditions. Slugs feed at night and hide in residue or soil during the day.
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Figure 4. Black Cutworm.

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Slugs are legless, soft-bodied, slimy, white, gray, or black gastropods (Figure 3). In corn, slugs scrape small strips in the leaf, leading first to window-pane damage and then leaf-shredding. In soybean, slugs create craters in the cotyledons and then ragged holes in the leaves. Slime trails are often seen in close association with their damage.
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White grub. True white grubs and masked chafer grubs can damage corn and soybean seedlings by feeding on plant roots. White grubs range in size from ¼ to over 1-inch long and have white bodies with tan to brown heads. White grub species can be distinguished from one another by the pattern of rasters (bristle-like hairs) on the tip of the abdomen.
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CORN INSECTS

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Wireworm (Elateridae spp.) larvae are hard, smooth, slender, and wire-like (Figure 3). The larvae vary from 3/4-(when young) to 1 1/2-inches long when mature and are yellowish-white to coppery colored with three pairs of small, thin legs behind the head. The last body segment is forked or notched. The larvae feed on corn seed and roots and can bore into the stalk just above the roots killing the growing point. Injured plants may show “dead heart,65533;? the death of the center leaves and stem, and may develop non-functional tillers. Damage may be more prominent in corn fields that were previously planted to small grains two to four years prior. As soil temperatures increase, the larvae move lower into the soil profile and become less of a feeding threat.
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Seedcorn beetle (Stenolophus lecontei Chaudoir) is a ground beetle that occasionally attacks corn seeds. This beetle is yellowish brown, 5/16-inch long, with a patch of black in the middle of each wing cover (Figure 3). Seedcorn beetle may feed on corn, preventing germination or reducing seed viability. Damaged seed will be hollowed out. They may also feed on the mesocotyl of emerging plants, causing stunting. No rescue treatments are available for the control of seedcorn beetles. In severe cases re-planting may be the only option.
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Black cutworm larvae vary from light-gray to black and grow to about 1 1/2 inches long (Figure 4). The larvae feed on corn at the base of the stem or underground, which can lead to clipping.
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