Timely identification of plant-parasitic nematode infestation in soil is an important first step in integrated management of nematodes that can damage corn, oats, soybeans, and other crops. You might not notice symptoms of nematode damage in plants during the first few years of an infestation but the damage can result, nonetheless, in lower yields. Also, symptoms of damage by many nematode species are nondescript and can be confused with symptoms of other stresses, such as herbicide injury, nutrient deficiency, compaction, etc. Here are three strategies to sample soil for plant-parasitic nematodes.
1. Sampling to scout for nematodes.
A scouting sample is necessary only for the soybean cyst nematode. Collect a scouting soil sample from areas of a field that are likely to have had the nematode introduced into the field in the past. Try to target specific areas, as shown in Figure 1. You can collect scouting soil samples any time of the year, but it is easiest after fall harvest or before spring planting.
2. Sampling to diagnose damage from specific nematodes.
Diagnostic soil samples, as the name implies, are useful for diagnosis of nematode damage to any crop species. A diagnostic soil sample is collected near plants that show symptoms of nematode damage, such as yellow or stunted foliage, and swellings or dead areas of root tissue. Collect 10 or more soil cores from within the root zone of plants that show the full range of symptoms, whether severe or just mildly affected. For a comparison, it often is useful to collect a similarly-sized soil sample from nearby plants that appear healthy. You can take a diagnostic sample any time when plants exhibit symptoms of possible nematode damage.
3. Sampling to predict potential for nematode damage.
Predictive sampling is used to estimate population densities and damage potential of plant-parasitic nematodes you know exist in a field. This information can help you decide on management strategies, such as use of nonhost crops or resistant host crop varieties. Predictive soil samples are most useful for estimating damage potential of soybean cyst nematode. It is difficult to predict whether damaging populations of other nematode species will develop on corn, oats, or alfalfa during the growing season based on numbers detected before the season begins. Ideally, predictive soil samples are taken in the fall after harvest, but also can be collected in the spring prior to planting. To get a good predictive sample, collect soil cores from 15 or more places within an area no larger than 20 acres. Sample the area in a systematic zigzag or M-shaped pattern.
For all three sampling strategies, a soil probe works best for collection, but a hand trowel or garden shovel also can be used. Place soil cores in a bucket and mix thoroughly. Then put the soil in a properly labeled plastic or paper soil sample bag.
You can submit samples to the Iowa State University Plant Disease Clinic or to private laboratories that offer nematode analysis of soil samples. A Plant Nematode Sample Submission Form must accompany all samples sent to the ISU clinic (ask for PD-32 at your county extension office). This form also contains additional information about collection of soil samples for nematode analysis.