Planting activity was proceeding at breakneck speed before the rains began, still many fields of soybean remain to be planted. Some soybean planting was rushed and 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 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 (look like a minature housefly) that are attracted to all types of decaying matter in which to lay their eggs. Soils planted too wet are often improperly sealed, 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. The problem will be worsened by cool-wet soils during the germination period.

Low rates of the neonicotinoid insecticides are on virtually all corn seed sold in Indiana and both are very effective on seedcorn maggot. On the other hand the majority of soybean seed is not treated with an insecticide and would be prone to damage if planted into weedy/manured fields. Should replanting be necessary, insecticide on the soybean seed is probably not necessary, as the seedcorn maggot will probably have already pupated and soon to emerge as an adult fly. In other words, the damage window will have closed.

Source:  Purdue University