Here's a situation that occurs in many areas in Illinois every year: The corn has come up, but in one or more areas of a field, it just doesn't "look right." Some plants may be stunted, yellow, or purplish. Root systems may be stunted or brushy, or even rotting. What's the problem? You can probably think of 10 things it could be.
Most of the time, nematodes are the last thing on the list of things to check as the cause of corn development problems. That's understandable, because nematodes don't cause specific symptoms and they're also hard to check for. The only way to diagnose nematode problems in corn is through soil samples analyzed by a qualified nematode testing lab. Many private labs will test for corn nematodes, as will the University of Illinois Plant Clinic; see its Web page at http://plantclinic.cropsci.uiuc.edu/index.html. Corn nematode control depends on the nematode species involved and how high its numbers are, so it's very important to get a reliable diagnosis.
In Illinois, when most people speak of "corn nematodes," they're talking about the needle nematode, which can cause severe damage. However, "corn nematodes" come in lots of different shapes, sizes, feeding habits, and propensity for damaging corn. For lots of good information, start with the University of Nebraska Web page at http://nematode.unl.edu/corn_nematodes.html. Be sure to click on the "links" link.--Terry Niblack