Nematodes
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.
Photograph 1: Bermudagrass rough damaged by nematodes.
Historically, nematodes are most often associated with warm season turfgrasses like bermudagrass, but are increasingly being found on cool season turfgrasses like creeping bentgrass annual bluegrass. In turf nematode damage is often associated with sandy or sandy loam soils.
Photograph 2: Nematode damage to a 'Tifdwarf' bermudgrass green
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. Symptoms appear in large irregular shaped patches because nematodes have a clump verse random soil distribution. Conditions that generally favor 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 great 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.
Photograph 3: Nematode symptoms on a annual bluegrass/creeping bentgrass green.
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. The greater the plant stress the fewer number of pathogenic nematodes needed to cause injury.
The management and control of nematodes is difficult. Culturally, emphasis should be placed on maintaining a healthy turf. Specifically, if nematodes have caused extensive root damage, light frequent irrigation should be practiced to minimize moisture stress. Fertility should be focused on foliar programs during the stress period. Options for chemical control are few. If nematode populations become high with associated turf damage nematicides like Divanem®
Although there are several pathogenic nematodes, a few of the more devastating or potentially devastating ones are mentioned below.
Sting (Belonalaimus) – considered the most damaging nematode on turfgrasses. It is known to cause damage to bermudagrass 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. In the United States the sting nematode is beginning to cause damage on creeping bentgrass greens.
Lance (Hoplolaimus)– is the most common nematode problem on putting greens in the United States. 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 (Meloidogyne)– 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 4: Root knot nematode
About the author
Dr. Karl Danneberger is a professor of Turfgrass Science at The Ohio State University. Dr. Danneberger's contact information can be found here. You may also follow Dr. Danneberger on Twitter: