Seedcorn maggot potential for planted soybean
click image to zoomSeedcorn maggot damage expressed after emergence. Now that corn planting is almost complete, soybean planting activity has been at breakneck speed. Some planting occurred in fields that had less than ideal seedbeds, meaning little to no weed control had been applied. Corn and soybean seeds planted in high crop residue, weedy growth, and/or where animal manure was applied are most often subject to attack by seedcorn maggot. You are probably familiar with the many drawbacks of planting into weedy fields, such as black cutworm, but seedcorn maggot is a potentially serious pest that is often forgotten.
Seedcorn maggot adults are small, extremely common flies that are found virtually everywhere and seldom noticed. They look like a housefly, but about 2/3 of the size. They are attracted to all types of decaying matter to lay eggs; maggots feed on rotting vegetation. Soils planted too wet often have open seed slots, attracting flies to climb down into the furrow and deposit eggs in decaying weeds next to the seed. Soon the yellowish-white maggots, up to 1/4 inch long, burrow into the seeds or underground portion of plants and feed. The damage they cause can serve as an entry point for a range of other pests as well, including fungal and bacterial pathogens. All of this happens beneath the soil surface, so the damage is usually first observed as skips in the row where plants do not emerge, or if they emerge, die back soon after.
click image to zoomSeedcorn maggot pupa, damage is done! Some soybean seed treated with low rates of Cruiser or Poncho will offer some protection if planted into weedy/manured fields. Should replanting be necessary, insecticide on the soybean seed (i.e., Cruiser or Gaucho) is probably not necessary, as the seedcorn maggot will probably have already pupated and soon to emerge as an adult fly, meaning the damage is done and risk of further infestations are extremely low.