Plant parasitic nematodes are small, microscopic, thread-like animals that utilize a stylet to puncture and feed from plant cells. In turf, these nematodes are root parasites. Nematodes are important turf pests, particularly in sandy native soils and coastal regions, but also in artificial, sand-based root zone mixes on putting greens or athletic fields.
Depending on the species of nematode and the numbers in soil, they are capable of contributing heavily to the decline of turf. However, many times weak turf is blamed on nematodes when poor cultural practices, fungi, insects, nutrient problems, soil compaction, poor drainage, or other environmental problems may be the more serious factor leading to the decline. All of these other stresses can also make nematode damage worse. Therefore, correct diagnosis is important to adequately address the problem and determine if the use of a nematicide is warranted.
Nematicides are generally highly restricted in their use and vary in their effectiveness against different species of nematodes. It is critical to carefully consult the label to be sure a product can be used on a particular site.
ABOVE GROUND SYMPTOMS: yellowing of turf initially, followed by wilting and slow recovery from wilt, poor response of turf to fertilization and eventual thinning in irregular shapes, followed by weed invasion. These symptoms occur over months and years.
ROOT SYMPTOMS: short, stubby roots with few branch roots compared to healthy roots. Roots may have a dark brown color, and sometimes (with sting or stubby root nematodes) exhibit swollen root tips. In sod with severe infestations, the sod strength is low.
SOIL SAMPLING: This is necessary for accurate diagnosis. Quart-size plastic bags can be obtained from the Cooperative Extension Service office in your county
The number of nematodes recovered from soil can vary greatly, depending on the time of year and the stage of crop or plant development at the time the samples are taken. Many other factors can be involved. Samples taken during the Winter and early Spring are less reliable, and in some situations certain nematodes may be missed entirely.
In general, for routine assays, sample during the time of year that the turf is growing. For warm-season turfgrasses, June or July is a good time to detect high populations is they exist. For cool season grasses, late spring or early summer should detect damaging populations, if they exist.
Diagnostic assays (those taken to determine if nematodes may be a factor) can be taken at any time: if high populations of damaging species are encountered, then certainly nematodes are a factor.
However, if nematodes are not found in damaging numbers, it still doesn’t preclude their role if the time of year the sample was taken is unfavorable for their survival. If nematode populations are high, determine the best approach to the problem including: improved turf management practices, planting new grass type, or chemical control.
A combination or integrated approach leads to the best success. Improve Turf Management Practices. Most grasses can withstand moderate numbers of most kinds of nematodes.
Deep, infrequent watering's encourage deeper rooting of the turf, allowing grass to obtain more water and nutrients than a turf having a short root system due to shallow, daily watering's.
Avoid excess nitrogen fertilization, as this encourages lush, succulent roots conducive to nematode population buildups.
Avoid stresses to turf such as mowing too short. Alleviate compacted soils and correct any nutrient deficiencies.
Plant a Different Grass. Planting another grass type may be a choice if the new grass provides acceptable quality and is adapted to the site. Sometimes nematodes are attacking a particular grass and damage is severe because it is not adapted to the site. However no variety of any turfgrass is known to have true resistance to all nematodes.
Using proper turf management practices and best adapted turf species is a more practical approach than simply switching varieties.