Corn Nematode Sampling

Corn Nematode Sampling

 Corn nematode (sting) damage in Nebraska field Corn nematode damage in Nebraska field
Figure 1. Severe sting nematode injury to corn. When sampling severely affected areas where roots have been severely damaged (1c, below),  collect samples from the perimeter edges of damaged spot(s) in the field to find the most nematodes. (Photos by Tamra Jackson-Ziems)

Sampling for Nematodes of Corn

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.
Nematode damage in corn
Figure 1c. Corn roots severely damaged by corn nematodes.

June 12, 2015

Plant parasitic nematodes are in every field to some extent, ranging from no obvious crop impact to severe injury and tremendous yield loss.  In soybean, the soybean cyst nematode is well-known and receiving a lot of attention in Nebraska as we monitor its spread to new areas. 

In contrast, 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.  

Timing is Important

The author discusses when and how to scout for corn nematodes. (CropWatch YouTube)

Corn nematode species are very diverse and not equally damaging. For example, those causing the worst injury, such as needle and sting nematodes (Figure 1), are relatively large and uncommon; damage will appear as noticeable spots in the field.  Because of their larger size, sting and needle nematodes are only present in fields with at least 80% sand. These nematodes are capable of moving deeper in the soil (up to several feet) as the season progresses and will move out of reach of traditional soil probes. For that reason, now may be the best time to sample sandy corn fields for nematodes while plants are small (up to approximately V6 growth stage). Early in the season these nematodes are expected to be shallow in the soil, feeding while corn roots are also shallow and mainly in the upper 8-10 inches of the soil profile. Sampling now should increase your chance of capturing them in a routine sample. 

Most fields have a mixture of several nematode species of varying population densities. Other nematode species affecting corn are not known to travel deeper in the soil, thus there is minimal risk from missing them during sampling later in the season. Fields with finer textured soils can be sampled for nematodes almost any time.  For example, sampling can be done early in the season when symptomatic areas are more obvious. Or, sampling can be delayed until after harvest, when nematodes will be at their highest population densities. Waiting until after harvest to sample may be more convenient for those who plan to collect soil samples for nutrient analyses and can simply collect additional soil to be used for both purposes.

 Corn field damaged by corn lesion nematode Corn lesion nematode root damage
Figure 2. Yellowing of plants (left) caused by root-lesion and other nematode injury. Yield in the center of these areas was as low as 30 bu/ac with badly damaged roots (right) near the end of the season.
 

Some nematodes, such as root-lesion (also called lesion nematodes), are much more common, occurring in more than 93% of Nebraska corn fields regardless of soil texture.  Lesion and other nematodes tend to cause less severe injury and symptoms (Figure 2) on corn than sting or needle nematodes. However, due to their wide distribution, the total losses they cause are probably greater than any other nematodes. 

Sampling Sandy Fields

Remember, the reliability of your diagnosis depends on the quality of the sample that you submit. The nematodes in your sample must stay alive from field to lab to achieve an effective analysis.
  • 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

Corn field damage due to low pH
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.

To Diagnose Symptomatic Areas. 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.

To Establish a 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.

More Information

For additional information see

Tamra Jackson-Ziems
Extension Plant Pathologist