The problem with many secondary insects, including wireworms and seed corn maggots, is that you don't know for sure when they show up. However, if they do show up they can do considerable damage to stands, often in patches, by chewing on roots and destroying young seedlings or the seed.
"They are more likely where lots of organic matter has been applied, such as heavy manure applications," says Mark Lawson, an agronomist with Syngenta, Danville, Ind. Seed corn maggot consist of larvae that emerge after small flies lay eggs. They are attracted to rotting organic matter and to fields where manure was applied.
There are no rescue treatments for either of these pests, Lawson says. If the pest shows up and thins the stand, your only recourse is to leave it or replant it. It may mean pulling out information and tables about when replant is likely to pay vs. when it may not pay. That may depend upon when the damage occurs, and the original planting date.
Most seed corn and about 90% of the soybean seed today carries an insecticide when it leaves the seed plant. Companies use different insecticides on corn seed, and on soybeans too, Lawson notes. You need to know what rate of insecticide is present on the seed. Unless the infestation of pests is very high, seed-coated insecticides should take care of secondary pests like wireworm and seed corn maggot.
Seed corn maggot can also attack soybeans. Some seed treatments for soybeans contain an insecticide and some don't. Again, you need to know if an insecticide is part of the treatment, and if so, at what rate, Lawson says. Your seedsman should be able to help you make this determination, no matter from which company you buy your soybeans. Make sure you know which insecticide, if any, is on the seed before you plant.