Nematodes
Egg -- Nematode eggs are microscopic (about 0.1 mm long), oval and transparent. Rootknot nematode eggs are laid in a mass of brown jelly. Other nematodes lay their eggs separately.
Larva -- Newly hatched to mature larvae resemble the adult stage (when not swollen with eggs) except for size (0.5 to 2 mm) and the lack of an exterior genital opening.
Host Plants -- Nematodes are found on most turfgrass species. Some species may cause severe damage. The ring nematode has been associated with decline of centipede grass and is often found in the soil around turf grasses. Spiral nematodes have been associated with damage to bluegrass and Bermudagrass. Sting nematodes may affect warm season grasses and bentgrass.
Damage -- Plant parasitic nematodes insert their stylets into the root cells and inject enzymes or other toxic substances. The cell contents are then sucked out by the nematode through the stylet. This feeding activity may cause surrounding plant cells to die or swell up (depending upon the species of nematode). Damaged roots may be more susceptible to other plant diseases. Affected plants are usually stunted, wilt in hot weather, develop nutrient deficiencies, respond poorly to fertilizers and may die during prolonged droughts. Damage is usually more severe in sandy soils and less severe in heavy clay soils.
Life History -- Many species of nematodes other than plant parasitic nematodes live in soil and water where they feed on other small animals (including other species of nematodes). Many nematodes are beneficial to the balance of nature in the soil ecosystem. Of the several hundred nematodes that feed on plants, relatively few damage turf grasses in the southeastern United States. Two of the most important nematode pests of turf, the sting and the stubby-root nematodes, feed externally on the outer surface of turf roots. The larval rootknot nematode penetrates into the root and causes a very small gall to form around it. As the rootknot nematode grows, its gall on the grass root grows also. Female rootknot nematodes never leave the galls, but lay their eggs in a jelly which is usually outside the root. The first stage larvae hatch inside the egg. Second stage larvae wriggle to the roots, penetrate into the growing tips and cause new galls to form as the nematode matures.
The larvae of all species of plant parasitic nematodes develop through four stages, molting between each stage. With the fourth molt, larvae become adults. After mating (not all species have to mate), eggs are laid (except in the case of the cyst nematode in which the eggs are retained in the body of the mother). The body of the cyst nematode mother forms a resistant cyst which can be carried on equipment or blown by the wind to infest new areas. Under favorable conditions (warm, moist soil and the presence of turf grass roots), development for most species may be completed in 3 to 4 weeks. In general, nematode populations are highest in late summer and fall and lowest in spring. Cold soil temperatures inhibit reproduction.
Nematicides for use on turf are contact types. Contact nematicides are usually applied as granules and washed into the soil where they dissolve. Nematodes are killed as they come into contact with the chemicals in the soil water. Fumigant nematicides now available vaporize slowly and kill nematodes as they come into contact with the gases in the soil.
Aerification of the turf before treatment will usually enhance control if drenches or granules are used. Otherwise these pesticides may not be able to penetrate through the thatch and soil to reach the nematodes.
Most nematicides also control insects and some relief from soil-inhabiting insect pests may result from nematode control efforts. Once a nematicide has been used, annual treatments may be necessary as certain nematodes may increase rapidly after treatment because of decreased competition and a rapid rate of reproduction. Nematicides should therefore be applied only when high quality cannot be maintained with good management practices and a nematode problem has been indicated by a soil assay. For specific chemical controls see the state agricultural extension service recommendations.