The success of the Nematode Advisory Program depends on the cooperation of the agricultural community, the Extension agents and the Nematode Assay Laboratory. Proper sampling, completion of appropriate forms, and careful laboratory analysis are all necessary to provide the grower with appropriate recommendations on nematode management. The Nematode Advisory Program can help growers avoid costly yield loss due to plant parasitic nematodes.
Sampling for Nematode Assays
The Virginia Tech Nematode Assay Laboratory currently performs assays for three different purposes:
- Predictive: The predictive assay determines if nematode populations at harvest are likely to affect the following crop. There is a fee for processing predictive samples. Checks should be made out to Treasurer, Virginia Tech and sent with the samples.
- Routine assays (for most crops): $11.00 per sample
- Routine plus cysts (usually for soybeans and tobacco): $19.00 per sample
- Diagnostic: The diagnostic assay determines if poor growth in the current year's crop is caused by nematodes. There is no fee for diagnostic samples.
- Research: The research assay determines nematode populations in soil from research plots. There is a fee for research samples. Contact the Nematode Assay Lab for further information.
The most appropriate time to sample depends on the crop and the purpose of the sample.
Predictive Assays: In most cases fall sampling provides the most reliable information for predicting nematode problems for a future crop. In general, nematode populations are highest at the end of the growing season and decline as the soil temperatures drop.
- Annual Crops: Sample at or immediately after harvest, September 15 to November 15.
- Orchards & Nurseries: For spring fumigation, sample between March 15 and April 30. For fall fumigation, sample during mid-season, July 15 to August 15.
- Turf & Ornamentals: Sample before planting.
Diagnostic Assays: Sample at the onset of symptoms, during the growing season. Nematodes feed only on living plants; therefore, sample soil around live plants showing symptoms. It is also helpful to send separate samples from healthy and diseased plants to compare population densities. Send soil including roots, if possible. Some nematodes spend part of their life cycle inside the roots and more accurate diagnosis of nematode damage can be made from samples including roots.
Always sample within the feeder-root zone; this varies for each crop. Avoid collecting samples when the soil is extremely dry or extremely wet. DO NOT add water to the soil after sampling. Sample areas of common crop history. For example, if one half of the field is planted to corn and the other half to soybean, sample each area separately.
- Collect vertical core subsamples of soil with a soil sampling core or shovel within the feeder-root zone. The depth of the feeder-root zone varies depending on the crop. For most annual crops and turf a 6" depth should be adequate. Nematodes do not occur uniformly throughout a field; thus, more than one subsample must be taken from the same field. The number of subsamples needed depends on the size of the field:
- For small fields (less than four acres), collect at least 20 subsamples.
- For large fields (more than four acres), divide the field into four-acre sections and collect at least 20 subsamples from each section. If the field consists of several soil types, divide the field into as many sections as there are soil types. Collect at least 20 subsamples from each section.
- Mix the subsamples in a clean bucket.
- Place at least one pint (500 cc) of the soil mixture into a nematode soil sample bag or plastic bag. LABEL COMPLETELY with the grower's name, address, county, agent, crop information, and field or sample number.
- Complete the appropriate form to send with the samples. The forms and nematode soil sample bags are available at Virginia Cooperative Extension offices at no charge:
- Nematode Soil Sample Bag -- Pub. 450-900
- Nematode Predictive Assay Report -- Pub. 450-098
- Nematode Diagnostic Assay Report -- Pub. 450-901
The sampling pattern for soil and root samples depends on the type of crop and the pattern of planting. Use the following guidelines to determine the sampling location or pattern:
- For solid-seeded crops, collect at least 20 subsamples from each four-acre section. Refer to Figure A.
- For row crops, collect subsamples from the feeder-root zone within the rows. Refer to Figure B.
- For established perennials, collect two subsamples from the dripline of each plant. Refer to Figure C.
- For single plants e.g. trees or shrubs, collect ten subsamples: five near the trunk and five from the dripline. Refer to Figure D.
Mail samples with the appropriate form, and a check for predictive assays, immediately to the following address:
Nematode Assay Laboratory
115 Price Hall
170 Drillfield Drive
Blacksburg, VA 24061-0331
Use Nematode Diagnostic Assay Report, Pub.450-901, available through local Extension offices.
- Diagnostic nematode samples
- Predictive nematode samples
- Nematode Threshold Densities
Nematode Assay Laboratory