Soil Sampling

In addition to monitoring visual symptoms, collecting soil samples is an effective method to determine if fields have nematodes. Once the presence of nematodes is determined, growers can develop the appropriate management program. Soil sampling can help producers determine if stunted plant growth is due to nematodes or nutrient deficiencies.

Soil sampling is only a tool, and results can be extremely variable due to sampling depth and location. Its accuracy is not guaranteed as nematode populations can be erratic throughout a field. For a more accurate representation of nematode populations, it is recommended that field histories and past crop rotations be considered along with current soil samples.

According to the University of Idaho Extension, an accurate diagnosis is vital if a producer is to make the appropriate management decisions, which makes proper sample collection, handling, labeling, packaging and shipment of the utmost importance. Below are five guidelines potato growers should follow when collecting soil samples.

1. Sampling should be done before any treatment or management decision is made and before planting to determine nematode levels. Midseason and post-treatment sampling also should be conducted before planting to establish the current and remaining nematode populations. Growers should utilize this information to determine the need for additional management options.
2. Sampling should occur when nematodes are active and at high populations.
3. Soil should be moist, but not excessively wet or frozen.
4. If nematicides are applied to manage a known nematode problem, samples should be taken following application, but before planting to determine the effectiveness of the treatment.
5. The best time for nematode sampling is usually the early fall.

When soils or fields allow, composite soil samples should be taken at depths of zero to 12 inches, 12 to 24 inches, and 24 to 36 inches to provide the most accurate information on potential infestations.

The size of the soil sample is based on the number of cores taken. The accuracy of the nematode estimate can be improved by increasing the number of cores in the sample. Growers should place cores from within a certain area into a clean bucket and thoroughly mix the cores, submitting 1 quart for processing. One sample should contain at least 20 individual cores and will represent up to 5 acres of uniform area. Place the sample in a bag that will retain the soil moisture, and identify the sample with a tag on the outside of the bag. Samples should be kept at 50 to 55 F, with an insulated cooler providing good protection. Using established university recommendations, deliver the sample immediately to the appropriate laboratory using an express delivery option. Always use a credible lab to ensure proper sample evaluation.

If the nematode population in the soil is high enough that the crop may be damaged, or if any nematode damage is detected in the tubers, the potatoes should be harvested immediately. Do not store nematode-infested tubers.

Certain background information should be included when submitting samples. They include:

Producers may submit soil samples to the following nematode diagnostic laboratories:

Idaho
University of Idaho-Parma Extension Research Station
29603 U of I Lane
Parma, ID  83660-0669
208-722-6701 phone
208-722-6708 fax
website 

Western Laboratories, Inc.
P.O. Box 1020
Parma, ID  83660
800-658-3858 phone
208-722-6550 fax
website

Oregon
Oregon State University
Central Analytical Laboratory
3017 Ag & Life Science Building
Corvallis, OR  97331-7306
541-737-2441 phone
541-737-5725 fax
website

Washington
Washington State University Prosser IAREC
24106 N. Bunn Road
Prosser, WA  99350-8694
509-786-2226 phone
509-786-9370 fax
website

Ever-Green Nematode Testing Labs, Inc.
36631 N. 19th Ave.
Phoenix, AZ  85086
623-465-5046 phone

Northwest Nema-Lab, Inc.
1126 Playfield Ave.
Prosser, WA  99350
509-786-3682 phone