Sampling corn fields for nematodes
Note that laboratories should extract nematodes from the soil, as well as endoparasitic nematodes (such as lesion nematodes) from root material. It is a good idea to contact your lab to determine what kind of sample they need. It is necessary for the nematodes to be alive in these samples because they must crawl out of root material during one of the extraction procedures. For this reason, it takes several days longer to process corn nematode samples than it does other types of samples.
Know Your Sampling Strategy
How you sample should be determined by your reason for sampling.
Diagnosing Symptomatic Areas. Nematodes can cause many types of symptoms, such as stunting, yellowing, root lesions and deformity, etc., all of which can be confused with symptoms from other common causes such as pH extremes, nutrient imbalances, insect or herbicide injury. This has frequently led to misdiagnoses.
Samples can be collected directly from symptomatic areas of a field; however, when a severely affected area is sampled, avoid sampling the center of the area where few roots and nematodes will be found. Instead, collect samples around the perimeter where symptoms are less severe and you are more likely to find more nematodes. It’s also a good idea when trying to diagnose a problem area in a field to collect a second sample from a nearby field that is apparently healthy. Analyzing both samples for plant parasitic nematodes will allow for comparison of nematode populations and a more definitive conclusion.
Establishing a Baseline. If you don’t have a particular problem spot in a field, you may still want to collect a sample for analysis if the yield has not been as high as expected and other possible causes, such as fertility issues and other pests, have been ruled out, or you are just curious about what nematodes are present. In this case, the most effective sampling strategy would be to collect a random pattern of soil cores from less than 40 acres to give a composite sample.
Testing Nematicides. The recent introduction of new seed treatment nematicides such as Avicta and VOTiVO is providing new management tools. One of the best ways to evaluate the product(s) on your own farm is to conduct your own replicated strip trial. However, they can be complicated and labor intensive. Their ultimate success and whether they provide the information you need will depend on how well you’ve planned them as well as some conditions that may be out of your control.