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Plant parasitic nematodes are microscopic worm-like organisms that require water to survive and are sensitive to high temperature. Only alive nematodes can be extracted from roots. Sampling might appear trivial but we believe proper sampling is the most crucial step in correct diagnosis.

General points to consider when sampling for most plant parasitic nematodes:

  • Use table below as the guideline on best time of the year to sample.
  • Put a label on the outside of each bag with the field name or sample description.
  • Keep samples cool; do not allow samples to dry out, and do not add water.
  • Do not allow samples to sit in the sun or closed automobile on hot and sunny days.
  • Mail them in a sturdy box as soon as possible.

Even though procedures for sampling among the most plant parasitic nematodes are similar, but there are differences based on the host and the type of nematodes we are trying to extract.

  • Corn parasitic nematodes: There are three major groups of nematodes that parasitize corn.
  • Endo-parasites (Lesion nematodes): These nematodes mostly feed within corn roots. Plant roots along with a soil sample must be submitted to recover these types of nematodes. A proper soil sample consists of about one quart of sub-samples taken directly from the root zone of affected corn plants, about 6-8 inches deep. Dig stunted plants and place adhering soil and roots in a plastic bag. Attach a label to the outside of the bag. On the label, give sufficient information to identify the sample. Root and soil samples should not become dry or get exposed to high temperature. The best time to samples for these nematodes is mid-season when most of the nematodes have migrated inside of the roots. These nematodes continue to feed through the growing season. They can be found in all kinds of soil types.
  • Ecto-parasites (Needle nematodes): These types of nematodes feed from outside of the young roots. The sampling procedure is the same as described earlier for Lesion nematodes. But, needle nematode is mostly problem in sandy soil and can be found early in the season (4-6 weeks after germination). Often they disappear when soil temperature rises above 80.
  • Semi endo-parasites (Lance nematode): These nematodes can feed from inside or outside of the roots. The sampling procedure is the same as the one described earlier for endo-parasites. Lance nematode feed throughout the season, has no soil type preference and can parasitize corn or soybean.
  • Soybean parasitic nematodes: Lesion and lance nematodes parasitize soybean too but Needle nematode does not. The sampling procedure for these nematodes in soybean is similar to the one described for corn. However, the most economically important nematode affecting soybean is the soybean cyst nematode (SCN). To determine SCN field population levels, one quart of soil should be collected for every 10 acres. Place small quantities of soil, collected in a zig-zag pattern, in a bucket. Soil can be collected by using a sampling tube, trowel or small shovel.  Soil should be obtained from the root zone, 4-6 inches, in a manner similar to that followed for soil fertility samples. If the accumulated volume of soil is greater than a quart, mix thoroughly and take a quart sub-sample for submission. SCN samples can be collected year around and regardless of the type of crop growing. The SCN distribution, as in most of the plant parasitic nematodes, is in patches. So, it is very important to take many sub-samples to increase possibility of hitting the concentrated area. One sample for every 10 acres is ideal. A quart of soil is sufficient and no root sample is required for the SCN. Samples can be taken anytime.
  • Pinewood nematode:  PWN causes a very rapid decline of pine. Needles, which are retained by dead trees, often have a tinge of green with a reddish brown cast to them. A sample of wood is needed to determine whether a pine tree has been killed by this nematode. A 6-8 inch long section of branch, at least 1-inch in diameter, taken from a location near the main trunk or several plugs of wood, taken with an increment borer from the trunk at breast height, are suitable for recovery of these nematodes.
  • Foliar nematodes:  If damage by foliar nematodes is suspected, collect both healthy and abnormal leaves and place them between dry paper towels for mailing. Keep samples separate and label with identification.
  • Turf nematodes:  Several plant parasitic nematodes can be major contributors in decline of turf, especially if ground is under other stresses. Core samples must be taken from suspected area as well as healthy turf area for comparison. Samples should not be exposed to high heat or drought.

Table 1. Recommended optimum sampling type and time for major plant parasitic nematodes in Indiana.

Host

Nematode

Sample

Sample Time

Corn

Needle

Soil & roots

June-mid July

Corn

Lesion, Lance

Soil & roots

Late June-Late Aug.

Soybean

Lesion, Lance

Soil & roots

Late June-Late Aug.

Soybean

SCN

Soil

Anytime

Turf

All

Soil & roots

June & Sept.

Melons

Root knot

Roots

At harvest

Mint

Lesion

Roots & soil

Late June-Sept.

Mint

Needle

Roots & soil

Late Spring or early fall

Mint

Root knot

Roots

Fall