Nematodes

Plant-parasitic nematodes are microscopic roundworms that feed exclusively on plant tissues. Most species parasitize plant roots. They survive in soil and plant tissues, and several different species may coexist in turf. They have a wide host range and vary in their environmental requirements and in the symptoms they cause. While the other species occur throughout the state, the sting nematode has only been reported from the Coachella Valley, and the seed and leaf gall nematode has only been found in Monterey and San Francisco Bay areas.

Several genera of nematodes may be associated with turfgrasses in California. Statewide, root-knot nematode is thought to be the most widespread and most damaging. Of the root-knot species, Meloidogyne naasi in particular prefers grasses over other hosts, and infestations of this nematode can reduce the growth and vigor of turfgrasses.

In 1992, sting nematode, a major pest of turf and other commercial crops in the southeastern United States, was collected from several turf sites in the Coachella Valley. Sting nematode feeds on the tips and along the sides of the roots. Activity of this pest is highest in sandy, moist soils when soil temperature is in the 72° to 92°F range.

Many golf courses in the Monterey and San Francisco areas with annual bluegrass (Poa annua) greens are infested with the seed and leaf gall nematode. Presence of this nematode is associated with localized yellowing and death of turf on greens. Root-knot, spiral, and ring nematodes are also commonly present on these courses.

Although not proven to be damaging to turf, lesion nematodes are commonly found associated with turfgrasses; stubby root nematode may be found feeding on growing root tips. Additional nematodes associated with turfgrasses in California are: dagger nematodes, Xiphinema sp.; needle nematodes, Longidorus sp.; pin nematodes, Paratylenchus sp.; and sheath nematodes, Hemicycliophora sp.

The symptoms described below are indicative of a nematode problem but are not diagnostic because they could result from other causes as well. Infestations may occur without causing any aboveground symptoms. Aboveground symptoms of a severe nematode infestation include patches of yellow plants, stunting, and poor growth. Feeding by root-knot nematodes results in swellings, called galls, on roots. Severely galled roots may appear malformed and the root system shortened and thickened.

Turf affected by sting nematode exhibits drought and malnutrition (yellowing) symptoms and does not respond to watering or feeding. Badly affected plants collapse and die in patches that can measure up to several feet in diameter.

Annual bluegrass infested with the seed and leaf gall nematode will have light-colored swellings or galls at the crown of the plant. Galls contain nematodes of different stages. Mature galls may be filled with hundreds of juvenile nematodes or with bacteria that resembles white cream.

Roots of grasses infested with lesion nematodes may exhibit brown-black lesions of various sizes and shapes. Feeding by stubby root nematodes causes swollen and/or discolored root tips and restricts root growth.

To make management decisions, it is important to know the nematode species present. If nematode species have not previously been identified, take soil and plant samples and send them to a diagnostic laboratory for identification.

In established turf, randomly take several soil cores (1 to 2 inches in diameter) or a cup cutter core to a depth of 4 to 6 inches, from each area of suspected nematode infestation. To allow comparison you may take similar samples from adjacent areas with apparently healthy plants. If only soil is present, randomly take several soil cores to a depth of 6 to 8 inches to make a composite sample of about 1 quart (1 liter) for each area. Place the samples in separate plastic bags, seal them, and place a label on the outside with your name, address, location, the previous crop, and the grass you intend to grow. Keep samples cool (do not freeze), and transport as soon as possible to a diagnostic laboratory.

Clean soil from equipment with water before moving from infested to noninfested areas. Avoid introducing nematode-infested soil or sod into areas free of nematodes.

Turf and soil cannot be removed from Coachella Valley golf courses where sting nematode has been documented without notifying the Riverside County Agricultural Commissioner. Soil samples should only be sent to a laboratory authorized to run quarantine samples.

Apply a preplant treatment if sampling indicates that potentially damaging nematodes are present. When treating established turf, leave a few of the affected areas untreated for comparison if possible.