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Now Is the Time to Sample for Plant-Parasitic Nematodes

May 3, 2002
Q. Who should take soil samples?

A. Every crop grown in Illinois may be affected by some species of plant-parasitic nematodes (PPNs). PPNs should not be the last thing on your list of things to check if you aren't getting the yields you want or expect from your crop. The most damaging PPNs in Illinois are, of course, the soybean cyst nematode and certain species of corn nematodes, but that's mostly because there are so many acres of those two crops. Even home- owners, with their crops of lawn and landscape plants, are subject to the depredations of PPNs on their high-value plants. The best time to take detection samples (those we use to detect whether a problem with PPNs might exist) is in the spring.

Q. What are the symptoms of PPN infestation?

A. If plant-parasitic nematode populations are high enough to reduce plant growth or yield, most plants will show nonspecific symptoms, meaning that you can't tell exactly what's wrong with the plants by looking at them. Soybeans, corn, vegetables, and other annual crops may show stunting or chlorosis. Perennials and trees may have an unthrifty appearance. It is important to note that these symptoms may not be obvious unless there are unaffected plants (resistant or unin-fected) nearby for comparison. PPNs are often referred to as "the hidden enemy" because they are difficult or impossible to diagnose in the field. The only way to tell if they're present in high enough numbers to cause damage is to submit a soil sample for microscopic analysis. If you had a mysterious problem with growth or yield last year or the year before, take samples this spring to see if the problem might be PPNs.

Q. Where should soil samples be taken?

A. For annual or perennial field crops, a soil sample should be taken in a zigzag pattern across a field. Most nematologists agree that one sample can adequately represent a 5-acre area; some say as high as 20 acres. So, what do you do if you have 300 acres? Collect samples from two or more arbitrarily selected 5-acre sections that represent similar soil types and crop histories. There's no need to sample the entire field for detection purposes. For individual plants, collect samples from the drip line of the plant, angling diagonally down into the root zone.

Q. How should soil samples be collected?

A. You'll need the following items: a soil coring tube (you can use any soil sampling device such as a trowel or shovel if a soil coring tube is not available); a bucket; sandwich-size, resealable plastic bags, one for each sample; a permanent marker; and a cooler. Collect about 20 soil cores (or scoops) from the sample area to a depth of 8 to 10 inches (see the previous paragraph for a description). Put each core into the bucket, and mix the cores thoroughly after all cores have been collected. Remove enough of the mixed sample to fill a plastic bag. Seal the bag and mark it with the permanent marker so that you'll know where the sample came from when the results come back. Place the sample in the cooler and keep it cool until you can pack it and ship it to a lab for analysis. Allowing the samples to heat up will effectively cook the nematodes in the soil and make it impossible for you to get a good analysis. If you're going to keep the samples for more than a day, put them in a refrigerator.

Q. Why should you sample in the spring?

A. Although it's true that the PPN populations will be highest in the fall, the damage they do depends on the number present in the spring when root growth begins. We can better predict the possibility of PPN injury if we know which ones and how many are present at the beginning of the growing season. You can, of course, take a sample any time. Once PPNs are established in a field, they're not going to go away. But they can be managed in most situations, if you know what and how many they are. We can help!

Q. Where should you send the samples for analysis?

A. Illinois has a number of soil testing labs that can do nematode analyses, especially for the soybean cyst nematode. The University of Illinois Plant Clinic can provide nematode analyses for any crop or home landscape plant (see http://www.cropsci.uiuc.edu/research/clinic/spe_frames.html).

For further information, call Terry Niblack at (217)244-5940 or e-mail tniblack@uiuc.edu.--Terry Niblack

Author: Terry Niblack Terry Niblack


The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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