Quality sampling for nematodes

Quality sampling for nematodes

Timing is important to a quality nematode analysis. In sandy fields sampling is best done up to the V6 growth stage. Fields with finer textured soils can be sampled for nematodes almost any time.

While soybean cyst nematode receives a lot of attention in some areas, nematodes feeding on corn roots already occur in every field to varying degrees and are usually simply referred to as "corn nematodes," although some may feed on other hosts, as well, including soybean, other crops, and some weed species.  There are more than 12 species of corn nematodes with common names such as sting, needle, stubby-root, lance, root-lesion, stunt, dagger, spiral, etc. Whether they cause serious crop injury and yield loss is determined by: which species are present in the field and their population densities. 

The only way to determine whether nematodes are a potential risk factor or causing damage is by collecting and submitting a sample(s) to a laboratory for plant parasitic nematode analysis.  It's important to collect, handle, and submit samples carefully to avoid compromising the quality of the sample (and reliability of the analysis).  University nematologists from across the country have worked to provide updated guidelines for collecting samples for nematode analyses from corn for diagnostic purposes and management recommendations.  This article describes the updated recommendations for collecting and submitting samples for nematode analysis for corn.  

Sampling sandy fields

  • Up to approximately V6 growth stage (within about four to eight weeks after  planting)
  • Plants
    • Collect 4-6 plants by carefully digging roots
  • Soil
    • Probe at an angle through root zone.
    • Probe at least 6-8 inches deep.
    • Take approximately 20 soil cores.
    • Collect a total sample size of at least 2 cups.
  • Samples should represent less than 40 acres.
  • Double bag in sealable zipper-top plastic bags.
    • Bag soil and plants separately.
  • Handle gently to avoid rupturing nematodes.
  • Refrigerate if possible until shipping.
  • Package with soft packing material in a sturdy leak-proof container.
  • If submitting your sample to the UNL P&PDC, print and fill out a Sample Submission Form indicating that the sample is for corn nematode analysis.
  • Ship early in the week, Monday-Wednesday
  • If sampling outside of Nebraska, please contact the UNL P&PDC for further instructions.

Sampling all other fields (not sandy)

  • Up to approximately V6 growth stage (within about four to eight weeks after  planting)
  • Otherwise, sampling can be delayed until after harvest when collecting other soil samples for nutrient analyses. 
  • Plants
    • If sampling by V6, collect four to six plants by carefully digging roots.
    • If sampling after V6, collecting additional roots is not necessary if soil cores are collected from the root zone.
  • Soil
    • Probe at an angle through root zone.
    • Probe at least 6-8" deep.
    • Approximately 20 soil cores needed.
    • Collect a total sample size of at least 2 cups.
  • Samples should represent less than 40 acres
  • Double bag in sealable zipper-top plastic bags.
    • Bag soil and plants separately.
  • Handle gently to avoid rupturing nematodes.
  • If possible, refrigerate until shipping.
  • Package with soft packing material in a sturdy leak-proof container.
  • If submitting your sample to the UNL P&PDC, print and fill out a Sample Submission Form indicating in the blank area that the sample is for corn nematode analysis.
  • Ship early in the week, Monday-Wednesday.
  • If sampling outside of Nebraska, please contact the UNL P&PDC for further instructions.

Laboratory preferences

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 diagnostic laboratory 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 other types of samples. Remember, the reliability of your diagnosis depends on the quality of the sample that you submit!  And, the nematodes in your sample must be alive for an effective analysis.

Sampling strategy

Figure 3. Symptoms of low soil pH (4.4 pictured here) and aluminum toxicity can be easily mistaken for nematode injury. Additional testing is necessary to confirm some problems.

How you sample should be determined by your reason for sampling.

Diagnosis

Nematodes can cause many types of symptoms, such as stunting, yellowing, root lesions and deformity, etc., all of which are often confused with symptoms caused by other common problems such as pH extremes (Figure 3), nutrient imbalances, and insect or herbicide injury. Thus, they are frequently misdiagnosed. 

Samples can be collected directly from symptomatic areas of a field, such as those pictured in Figure 2.  However, when sampling a severely affected area, such as that illustrated in Figure 1, 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, apparently healthy area of the field.  Having both samples analyzed for plant parasitic nematodes will allow for comparison of nematode populations and a more definitive conclusion.

Baseline

If you don't have a particular problem spot in a field, but yield has not been as high as expected and other possible causes, such as fertility, other pests, etc. have been ruled out, you may want to collect a sample for analysis. In this case, a composite sample from a random pattern of soil cores collected from less than 40 acres would be the most effective strategy. 

Testing nematicides

The recent introduction of new seed treatment nematicides, such as Avicta and Votivo, is providing new management options and many growers have expressed interest in trying these new products. One of the best ways to evaluate the product(s) on your own farm is to conduct your own replicated strip trial, which many producers have chosen to do.  However, this process can be complicated and labor intensive. The ultimate success of these strip tests to answer your questions is determined by how well you've planned them and sometimes by conditions outside your control.  

Commercial product testing usually occurs over several years and across hundreds of locations to help minimize the impacts of variability. Testing conducted in just one to several locations over one to two crop seasons may not provide adequate information to reflect how the product will perform and may be of limited value during some years or situations. 

If you decide to conduct your own testing, you will need to collect yield data from replicated (multiple) strips (either with a yield monitor or weigh wagon) of at least three strips per treatment to account for the variability within a field. In addition, many people have expressed interest in sampling for nematodes within treatment strips to evaluate product performance on their farm. 

Samples collected for corn nematode analysis can be processed at the UNL Plant and Pest Diagnostic Clinic for a fee of $40 per sample.  Because of the variability among laboratory procedures, you should contact your lab of choice to find out what they require for sample submission. 

Read the full post from University of Nebraska-Lincoln here, including information on the timing of when samples should be pulled.

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