No. 4 Article 6/April 29, 2010

Time to Plan for Corn Nematode Sampling

Nematodes are probably a much bigger problem for corn growers than we've thought before. For example, in our 2009 corn nematode survey, we found that about half of the cornfields in Illinois have lesion nematode population densities at or above the threshold for moderate to severe risk of injury (yield loss). Lesion nematodes are capable of injuring corn roots by themselves, and they are also frequently involved in the development of root rots.

The best time to sample for diagnosis is about 4 to 6 weeks after planting. A couple of weeks more or less may not matter very much, but it's time to put sampling on your calendar now.

Corn injury caused by nematodes cannot be diagnosed from symptoms. The symptoms of nematode parasitism can look like those caused by other production problems, including poor or uneven crop development, yellowing or streaking, and reduced or brushy root systems. The only way to diagnose corn nematode is by direct examination of the worms under a microscope following an appropriate extraction method. Some private labs will analyze soil for corn nematodes, as will the University of Illinois Plant Clinic. The Nematology Lab also does corn nematode analysis; contact me for more information ( Both the Plant Clinic and the Nematology Lab charge $40 for a corn nematode analysis.

Exactly how and where you sample is determined by the reason you're sampling. Corn nematode management depends on the species involved and how high their numbers are, so it's very important to get a good sample as the basis for a reliable diagnosis. Typically you just want to know whether nematodes are causing yield loss in a given field. Start with how the plants look:

Other things to consider for sampling:

Again: corn nematode management depends on the species and population densities in the field. A good sample will result in a reliable diagnosis and management recommendations.--Terry Niblack

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