Plant parasitic nematodes are small roundworms, invisible to the unaided eye, that live in the soil and on the roots of plants. They feed on the cell sap of roots by piercing the root with a spearlike mouth part similar to a hypodermic needle. Feeding by nematodes may destroy many of the feeder roots, curtailing the ability of the grass plant to obtain minerals and water from the soil. The feeding wounds produced by nematodes are used by some fungi to gain entry into the interior of the roots, causing root-decay diseases.
The majority of soil nematodes are free living, do not possess a spearlike mouth part, and do not feed on plant roots. These beneficial nematodes feed on dead organic matter, fungi, and insects in the soil.
Symptoms of nematode injury are similar to those associated with poor soil fertility. Nematode-infected plants exhibit these symptoms, not because the nutrients are lacking in the soil, but because the roots have been destroyed by nematodes or because the nematodes are taking nutrients needed by the plant as they feed. If soil is of satisfactory structure and texture but poor growth, off-coloring, and thinning of turf occurs and the turf does not respond to fertilization, there is a possibility that nematodes are involved.
Soil in the root zones of grass plants just beginning to decline is more likely to contain parasitic nematodes than is soil around dead or nearly dead grass plants. Nematodes are easiest to detect in mid- to late summer when their populations are the highest. Accurate diagnosis of a nematode problem requires professional analysis and identification. Soil and root samples collected for nematode assay should be kept moist and cool until identification is completed. Samples collected from mid-October to May often show lower populations because the nematodes are in the egg stage and cannot be detected by normal sampling techniques.
Vigorous turfgrass is less likely to show damage from nematode injury. However, knowledge of the many factors influencing nematode population levels in northeastern United States is so limited that distinct cultural practice recommendations are not possible.
Nematicides are available as highly toxic fumigants and drenches. Chemical treatment may be undertaken only by professional pesticide applicators and only after professional diagnosis shows nematodes to be the problem.