Issue No. 12, Article 3/June 13, 2008
Corn Nematodes Thriving in Illinois
As if corn growers don't have enough problems this year, numerous reports from southern and central Illinois suggest that corn nematodes are thriving under the conditions we've had so far this spring. Based on purely anecdotal evidence (observations by me and Jason Bond, plant pathologist/nematologist at Southern Illinois University), the problems are most severe in sandy soils and involve four types of nematodes: needle, dagger, stubby root, and sting. In heavier soils, lance nematodes appear to be much more abundant this year than usual. Some excellent photographs of symptoms of corn nematode injury, taken last week in southern Illinois, are available at www.scnresearch.info/disease_photos/.
Symptoms of corn nematode injury are nonspecific (stunting and/or yellowing), as you can see from the photos, but affected plants occur in oval patches, often elongated in the direction of tillage. Roots may appear perfectly healthy but stunted, completely rotten, or anything in between. There are no diagnostic symptoms that you can use in the field. The only way to diagnose corn nematode injury is by having a qualified lab extract and identify the nematodes from a soil sample, preferably one containing root tissue.
Sampling for corn nematode diagnosis is not difficult when the soil is wet and plants are in the early growth stages. Sample with a 1-inch diameter soil probe, targeting the edges of the affected patch of yellowed or stunted plants (plants in the middle of such a patch may be too damaged to support many nematodes). Sample healthy-looking plants away from the affected area as well, to provide a comparison. Sample in the root zone, about 12 inches deep, and take 20 or so cores. Carefully combine the cores into one sample in a plastic bag, and place bagged samples in a box insulated with crumbled newspaper or something similar to protect the samples from overheating and bumping. Some corn nematodes are extremely sensitive to mishandling.
Corn nematode management depends on the nematode species involved and how high the numbers are, so it's very important to take a good sample and get a reliable diagnosis. Many private labs will test for corn nematodes, as will my lab and the University of Illinois Plant Clinic; see their web page at plantclinic.cropsci.uiuc.edu/submit.html.