Forty fields under cotton cultivation in the Mississippi Delta were assayed for the presence of plant parasitic nematodes. Soil samples were taken at harvest from four locations under center pivot irrigation and from four adjacent nonirrigated locations. Samples were assayed using a semi-automatic elutriator-centrifugal sugar flotation method and were bioassayed using the root knot susceptible tomato cultivar 'Floradel' and the cotton cultivar 'Rowden'. For the bioassay, three pots containing 500 cc of soil from each location were planted with seed of each of the susceptible cotton and tomato cultivars. Activated charcoal (0.4% v/v) was added to the soil in which the tomatoes were grown to reduce herbicide injury. The assay plants were grown in the greenhouse at temperatures that ranged from 20 to 35 C. The plants were harvested at 60 days, the roots were washed, and observed for the presence of galls.

Reniform nematodes were recovered from soil samples from at least one location in 17.5% of the irrigated and nonirrigated locations. Numbers of Reniform nematodes recovered per pint of soil averaged 4184 from nonirriqated and 24,197 from irrigated plots.

Root knot nematodes were recovered from soil samples from at least one location in 35% of the irrigated and 32.5% of the nonirrigated locations. The number of root knot nematodes per pint of soil averaged 226 from nonirrigated plots and 440 from irrigated plots. Root knot galls were observed on tomatoes grown in soil from at least one plot in 27.5% of the locations. Root knot galls were observed on cotton grown in soil from at least one plot in 29.3% of the locations.