Random patches of wilted turfgrass that are unresponsive to irrigation, assume a gray/green appearance and then turn tan/brown just before dying MAY be suffering from nematodes. These symptoms are somewhat characteristic of several diseases, insect infestations and even environmental stresses, so when making a determination, all possible causes must be considered. The symptoms of nematode injury are more apparent when turf is under stress. Bear in mind that plants weakened by nematodes are more vulnerable to other pests as well.
There are several species of plant parasitic nematodes associated with turf in Indiana. These microscopic soil organisms are not visible to the naked eye and must be isolated from soil around the root area by special laboratory methods. Most common nematode species that cause damage to golf courses in Indiana include: Ring Nematode, Stunt Nematode and Lance Nematode. Most recently, however, a turf sample was found to be infested with root knot nematode. Although this is a major pest of turf in the southern states, it is most likely an isolated case in Indiana.
When questions arise, it may pay to take soil samples. Soil samples need to be taken to a root-depth of 4 inches with soil probes. The accuracy of the determination increases as more sub-samples are taken. A minimum of a pint of soil is required for nematode analysis. A sample from a “symptom -free” area and a comparable sample from an area where symptoms are obvious, is recommended in order to better diagnose the problem.
Remember that nematodes are live organisms. Soil samples should not be exposed to high temperature and should not be allowed to dry, as nematodes will not survive these conditions. Forward samples to the Nematology Laboratory (765-494-5901) at Purdue University, Department of Entomology, Smith Hall, 901 W. State Street, West Lafayette, IN 47907-2089. There is a $10 charge/sample for nematode analysis. If nematodes are confirmed, the best management practice starts with eliminating stress and providing proper fertilization as much as possible. A restricted use pesticide, Nemacur, may be effective in controlling turfgrass parasitic nematodes, however, it’s turf registration either has been revoked or soon will be cancelled. This puts even more pressure on turfgrass managers to maintain vigorous, well irrigated and fertilized, stress-free turfgrass.