Terry L. Niblack Professor Department of Crop Sciences (217) 244-5940; tniblack@illinois.edu

Corn Nematodes: An Old Problem is Coming Back to Haunt Us

Are you old enough to remember the days when corn nematodes created some of the most difficult problems in corn production? Because of the changes currently taking place in integrated pest management practices in corn production, we can expect corn nematode problems to increase. Search your memories for the things you used to see and look for, because you’re likely to see those same things again. Nematodes are the most frequently overlooked cause of corn disease. These tiny animals feed on corn roots and cause symptoms that could be blamed on many different kinds of stress (Fig. 1). They also can intensify expression of specific symptoms due to nutrient deficiency, herbicide injury, and other causes.

There are three myths about corn nematodes that should be explained right away.

Myth #1 is that corn nematodes only occur in sandy soils. Wrong!! Damage in sandy soils is more likely to be spectacular – dead or dying plants in the center of a large oval of stunted plants – but damage DOES occur in heavier soils. It’s usually misdiagnosed as nutrient deficiency or herbicide injury and it isn’t necessarily obvious – until harvest, that is.

Myth #2 is that corn nematode injury is rare. It isn’t! And it’s going to get worse as time goes by. The major contributing factors are: reduced tillage, use of GMO corn for insect control, and the changing chemistry of insecticide/nematicides.

Myth #3 is that “corn nematode” means one particular kind of nematode. It doesn’t! There are at least 4 major types of corn-parasitic nematodes that can seriously damage corn in Illinois.

· Lesion nematodes feed inside corn roots. Infected root systems have brown spots, or lesions, appearing on a few to most of the individual roots. Heavily infected roots will rot. As a result, lesion nematode injury (which occurs most frequently on heavier soils) is usually diagnosed as root rot – and the nematode cause is overlooked.
· Needle nematodes are devastating and, in high enough densities, can kill seedlings. The pictures you usually see of “corn nematode damage” are pictures of injury due to needle nematodes. Because these animals are large (as worms go), they are limited to sandy soils. In needle nematode-infested fields, grassy weed control is important because these nematodes can feed and maintain their populations on grassy weeds.
· Lance nematodes usually cause “hidden injury,” that is, subtle damage that is very difficult to detect from looking at the plants. These nematodes can feed from either the inside or outside of corn roots, and can predispose plants to other types of diseases.
· Dagger nematodes are some of the most common nematodes we see in corn nematode samples. Although they are large for nematodes, they are not limited to sandy soils and can cause damage in a wide range of soil types.

Control of corn-parasitic nematodes depends on proper diagnosis! Submit your corn samples to the Plant Clinic (see http://plantclinic.cropsci.illinois.edu) or a reliable private lab. Be on the lookout for increasing corn nematode damage, and don’t let nematodes remain the last thing on your corn production checklist!