Most plants are attacked by one or more types of nematodes. These parasites are microscopic worms that live in the soil and in plant roots. Nematodes cause several hundred million dollars in losses in the United States annually. In Kentucky, soybean cyst nematode is considered to be the most damaging nematode disease, causing annual losses of approximately 10 million dollars annually in soybeans. It may well be that if we could accurately measure losses from these pests, losses would be even higher. This is because nematode damage often goes unrecognized or is blamed on some other problem.
Most important nematodes feed on plant roots. This directly interferes with water and nutrient uptake. Root injury causes above-ground symptoms similar to those produced by other conditions that damage the root system. Plants frequently appear to be suffering from a lack of moisture or fertilizer, even when water and fertilizer are adequate. Typical above-ground symptoms are stunting, yellowing, loss of vigor, general decline and eventual death of plants when nematodes occur in high populations.
Nematode injury in the field is rarely uniform. Symptoms usually appear in small, scattered areas and are usually more obvious when soil moisture and fertility are low.
When nematodes are suspected, roots should always be examined and soil samples taken. Nematode symptoms on the roots depend on the type of nematode causing the injury. Usually the symptoms will be one or more of the following: galls or knots, tiny brown or black lesions, stubby roots and complete loss of feeder roots.
Many other problems can cause symptoms similar to nematodes. For this reason, samples need to be examined when nematode injury is suspected.
Nematodes are controlled with cultural practices such as crop rotation, resistant varieties and nematicides.