The best time to sample for parasitic, yield-robbing nematodes is in the fall, cotton specialists say.
“Nematode populations usually are low in the spring and build throughout the growing season to reach peak densities at harvest,” says Don Blasingame, a plant pathologist and nematologist.
“Nematode populations are easier to detect and estimates are more reliable at harvest than at any other time. Samples should be taken before cultivation when rows are still in place because the population is concentrated around the existing root zone.”
In general, a sample should represent about 10 acres of a similar soil type and should consist of at least 20 individual soil cores in that area, says Blasingame, a retired Extension specialist with Mississippi State University. “The greater the number of samples collected, the more accurate and reliable the estimate will be.”
Growers can use soil probes, steel tubes about 1 inch in diameter, to take the samples. Each soil core should be taken at a depth of 6 to 12 inches. The samples should be thoroughly mixed in a bucket and about a quart of the mixed soil placed in a plastic bag that can be sealed to inhibit drying.
Blasingame says nematode samples require special handling. “A nematode sample should not be handled like a soil fertility sample,” he notes. Nematodes are living creatures, and if a sample dries or is placed in the sun, the nematodes will die. The lab results will not accurately reflect the field situation.”
A nematode sample should be handled like a carton of milk, he says. “It should be kept cool, but not frozen. During sample collection, it is important to keep the soil sample in a cool location, such as an ice chest in the shade. It should be transported in a pre-cooled ice chest to prevent overheating.”
Deliver the samples to a diagnostic laboratory as soon as possible, says Blasingame. For information about the laboratory nearest you, contact your county Extension office.
Growers should also provide all pertinent information, such as current crop, past crop, intended crop, date of sampling, location, grower name, description of specific problems and nematodes suspected in the area with the sample.