Number of samples:
Nematodes are unequally distributed in golf greens and in soil in general. In order to get a good estimate of the population, take a minimum of 20 cores per green; 30 would be better. If you have a "bad sector" in the green, consider sampling the bad area separately from the "good" area; this will give you more confidence in the role that nematodes may or may not be contributing to the problem.
How deeply you sample will also affect the results. Nematodes are found primarily in the top 4 inches of soil, if you go deeper than 4 inches, the nematode population will appear lower. In some cases, if you only sample to a 2 inch depth, the population may appear higher; 4 inch depth is a compromise. Bulk the subsamples together and identify the location on the outside of the bag... paper notes put inside with the soil often deteriorate or the writing becomes illegible.
Time of the year to sample:
If you have a history of root-knot nematodes and want to assess their population, sample mid-April to mid-May; this is when the highest count of juvenile root-knot nematodes will occur. As the soil warms up, the juveniles will move into the roots and will not be extracted by the method that most labs use (wet sieving/sugar flotation). For ectoparasitic nematodes (which remain in the soil), you can start sampling the first week in June. If you sample in early May, the nematode count may appear higher because there are a lot of nematodes that have over-wintered but will not survive until June. As the season progresses, nematode populations generally increase until August, although this is a rough rule of thumb.
Tips to minimize damage to the green:
Use a small bucket to collect the sub samples (see picture below). After you pull the soil cores, tear off the top inch or so of turf/thatch (black arrows); drop the soil core into the bucket. Use a watering can (or other device) filled with dry top dressing to fill the holes to within about 1 inch. Place the turf/thatch piece into the hole and step on it to secure. If the plug sits higher than the surrounding turf, the mower will kick it out. An extra bonus to the nematology lab is that the soil is easier to process if the turf/thatch has been removed.
To submit samples to UMass for analysis, visit Turf Disease Diagnostics and Turf Nematode Assay and follow the instructions for nematode samples.
Mail or deliver samples to:
Robert Wick
Fernald Hall
270 Stockbridge Road
Amherst, MA 01003
Submitted by: Dr. Robert Wick