Below ground symptoms furnish the positive proof of root-knot problems. Affected roots have swellings or galls, ranging from very small pinhead size to one-half inch or more in diameter on the larger roots. These galls are enlargements of the root tissue and cannot be detached without breaking the root. If the roots are not knotted, but the above ground symptoms indicate a nematode problem, ask your county agent to take a soil sample in the root zone of the affected plants. He will send it to the Plant Disease Clinic, Four Towers Building, Cooperative Extension Service, The University of Georgia, Athens, GA, to be checked for other types of nematodes which may also damage beans.
Rotations have some value if a single species of nematodes is present.
If several genera or species are in a field, it is difficult to find a rotational crop that will not favor the buildup of at least one kind of nematode. Do not plant fall beans behind a root-knot susceptible crop, such as cucumbers, tobacco, cotton, squash, tomatoes, cantaloupes, peas or beans. Leaving the land fallow during the summer or planting rye in the field in the fall should reduce the root-knot nematode population. The application of a fumigant type nematicide in the row before planting is the best way to control nematodes in beans. Fumigants can be applied by a gravity-flow applicator, and should be placed 6 to 8 inches deep in the row.