Tech Notes Issue 1
Nematodes Contribute to Summer Stress Injury On Both Warm and Cool Season Putting Greens
Nematodes are extremely small (microscopic) translucent roundworms that are among the most abundant animals on Earth. No more than 10 percent of the genera are considered plant pathogenic. Given the abundance of nematodes, one can always find them in soils. Laboratory diagnosis is important in determining the nematode species present and in what numbers.
Although threshold numbers have been determined for many of the plant parasitic nematodes, the number needed to cause injury is dependent on the health of the plant. Nematode injury is often associated with turf under stress. The greater the plant stress the fewer number of pathogenic nematodes needed to cause injury.
Nematodes attack the turfgrass roots causing a reduction or loss of the root system. The result is the inability of the plant to take up water and nutrients. Symptoms often appear as moisture or nutrient deficiency leading to the thinning of the turf. Conditions that generally favour the growth and development of pathogenic plant nematodes include extended periods of moderate soil temperatures, and soils with a high sand texture. Symptom expression is greatest under high temperatures where the turfgrass plant is under stress, and restricted root systems cannot provide adequate moisture. High sand content soils can exasperate injury through poor water and nutrient holding capabilities.
There are several pathogenic nematodes, a few of the more devastating or potentially devastating ones are mentioned below.
Sting - considered the most damaging nematode on turfgrasses. It is known to cause damage to couchgrass at levels as low as 10 nematodes per 100 cc of soil. Sting nematodes feed on the tips of the roots producing large, girdling lesions and a short stubby root system. The sting nematode will also cause damage on creeping bentgrass greens.
Lance - is a common nematode problem on putting greens. These nematodes produce slight swelling and brown root lesions. The root systems appear to be rotting and lack root development. The turf symptoms appear as a general decline.
Root-knot - Primarily occurs on creeping bentgrass greens. Symptoms often appear as yellow patches on greens during periods of high temperature. Roots that are infected swell and galls are present. The roots become distorted brown or rotten in appearance.
Photograph: Nematode damage to Poa annua green.
Symptoms look like nutrient deficiency but no root system is present.