The soil is a battle zone that will largely determine the fate of your corn crop, says George Bird, a Michigan State University (MSU) nematologist. Both soil type and soil health are keys to microscopic worm (or nematode) population levels that influence whether or not corn roots start out strong during the growing season, he says.

While most corn growers understand the relationship between good soils, good root growth and good yields, not as many consider the battle going on underground that can either help or hinder their bottom line, says Bird. He points out that there are many different nematodes present in almost all corn fields – some are plant parasites that can cause significant damage and others are nonparasitic species that help boost root growth and yields (see sidebar on next page).

 “Beneficial nematodes make nitrogen (N) available to plants,” explains Bird. “They feed on soil bacteria and excrete N into the root zone in a plant-available form.”

Anything farmers can do to feed the soil bacteria – whether it be manure, or compost or cover crops or crop residue – will in turn provide more N for corn roots, he says.

In some instances, adding organic matter to soils has helped soil quality and reduced a crop’s susceptibility to plant-parasitic nematode damage, says Bird. Michigan potato growers have recently managed nematodes successfully by spreading compost over problem areas, “but not at high rates – just enough to act as a pulsing agent for the crop,” he says.

Different crops are susceptible to different plant-parasitic nematodes. There are three parasitic-nematode types that cause the most damage to corn in Michigan: needle, root lesion and stubby root, says Bird.

“If your corn has a nematode problem, the corn needle nematode is the worst one that you could get,” he says. “It can be disastrous for corn yields, but it’s usually limited to areas with coarse-textured, sandy soils.”

Unlike other nematodes that feed on corn, the corn needle nematode can be managed reasonably well through crop rotation, says Bird. “On one farm, we doubled the corn yield after rotating away from continuous corn to alfalfa, clover and soybeans,” he says.

The corn needle nematode also avoids warm soils, Bird adds. “They do their damage early in the season and then head deep into soils later on,” he says. “So, it’s best to scout for these nematodes and sample soils early in the spring.”

Other nematodes that feed on corn will either chew inside and remain in the roots (such as root-lesion nematodes) or stay closer to the soil surface where soil samples can detect them from early spring through late summer, says Bird. Crop damage from needle, sting and stubby root nematodes often resembles herbicide injury, he points out. He adds that the sting nematode has never been found on corn roots in Michigan, but that it is a severe problem in other corn-growing states.

Nebraska and Kansas have significant problems with sting nematodes that feed on corn, says Greg Tylka, Iowa State University Extension plant pathologist.

“The two most damaging nematodes to corn per individual worm are the sting and needle nematodes,” says Tylka. “Nebraska and Kansas seem to be ground zero for these two, which are extremely damaging and almost always occur only in sandy soils.”

All the other nematode types that feed on corn can be found in various soil types, he says.

While crop damage from sting and needle nematodes is typically obvious and dramatic, the injury to corn from other parasitic nematodes isn’t often recognizable, says Tylka. Other nematodes feeding on corn are stunted, yellow growth and general stress symptoms or some wilting under dry conditions, he says. “In general, the plant looks unthrifty.”