Figure 2. Seedcorn maggot
Soil insect pests are generally more of a problem on corn and soybeans than on small grains and forages. Soil-applied insecticides recommended for control of rootworm larvae also may prevent early stand losses due to wireworms, grubs, seedcorn maggot, and seedcorn beetles. If a soil-applied insecticide is used at planting, then a seed applied insecticide may not be necessary. Refer to the label of the soil-applied insecticide to determine which insects are controlled before purchasing a seed treatment insecticide. Stand losses to these soil insects is generally not significant enough to warrant routine use of soil-applied insecticides in first-year corn. The use of insecticide for first-year corn may change in the future due to a biotype of the western corn rootworm beetle. Benefits from suppression of early-season soil pests may be significant in 1) no-till or reduced-tillage conditions with poor weed control where a high risk exists for a given insect problem such as wireworms and grubs in corn following established sod, and 2) continuous corn where early-season pests may cause unacceptable stand losses.
Seedcorn maggot or the bean seed maggot are small, yellowish-white, legless fly larvae found feeding on corn seeds. Extensive feeding by these maggots will cause a reduction in stand. In general, seedcorn maggot problems are most likely to occur in situations where; 1) high organic matter or decaying vegetation attracts egg-laying adult flies (i.e. a green cover crop such as rye or alfalfa is plowed or disked under), and 2) cool, damp soil conditions delay seed germination and prolong the period vulnerable to maggot attack. No-till production systems have not been found to increase the likelihood of problems with seed maggots. Several products are formulated for application prior to planting seed on the farm as planter-box or hopper-box treatments.
Figure 2. Seedcorn maggot
Partially eaten seeds, loss of germination, or stunted seedlings in the presence of small (1/4 to 1/3 inch long) brown ground beetles indicate a seedcorn beetle problem. As with seedcorn maggots, damage is most likely to occur under cool, damp conditions where seed germination and seedling development are delayed.
Figure 3. Seedcorn beetle
Wireworms are the larval stage of the "click beetles." The term "wireworm" applies to a complex of species with life cycles requiring one or more years per generation. Wireworm populations affecting corn are most severe in fields following sod or fields having a prolonged grassy weed problem. The larvae pass through a number of life stages, or instars. The earliest stages are very small and white, the latter stages have a characteristic hard-shell appearance and are yellow-brown in color. Full-grown larvae range from 1/2 to 1 inch long depending on the species. Wireworms damage corn by feeding on germinating seeds and young seedlings and may bore into stalks at the soil level. Stand loss may be significant in fields with high populations. In fields where a soil-applied insecticide is not used, especially first year corn fields, application of seed treatment insecticide is strongly recommended.