There are almost 20,000 species of nematodes, or microscopic worms, making them the most abundant multicellular animals on earth. They feed on bacteria, fungi and other nematodes. Nematodes are often described as a tube within a tube, referring to the alimentary canal that extends from the mouth to the anus. They do not have a discrete circulatory or respiratory system.
Beneficial nematodes are introduced to lawns and grasses so that they will feed on bacteria, fungi and other organisms, such as grubs that feed on grass. They are a big part of organic lawn maintenance if you don't wish to use chemicals to kill lawn pests. They have a spear-like mouth that functions much like a hypodermic needle. The mouth punctures the organism's cells, allowing the nematode to lay eggs in the organism, thus killing the pest from the inside out.
Signs of Damage
Other nematodes cause damage; they destroy the roots, preventing the plant from obtaining water and nutrients. Nematode damage may show as irregularly shaped brown or yellow patches in lawns. Weeds such as spurge and sedge may appear, indicating nematode damage to the turf. Since many conditions can cause dead patches in lawns, the only way to accurately diagnose nematode infestation is by sending soil samples to a lab for testing.
Nematicides such as DBCP are now banned for use on home lawns. They were popular for treating nematodes in crops and nursery plants for many years, especially in the agricultural areas of California. In 1977, the United States Environmental Protection Agency (US EPA) banned nematicides because of evidence of infertility in men and induction of tumors in laboratory animals. Despite the ban, DBCP levels remain high in soil and continue to be a groundwater contaminant in areas of past high use, in particular California's Central Valley.
Good turf management practices must be used to promote healthy lawns. Adding organic matter such as shrimp and crab shells to the soil before planting helps increase antagonistic microorganisms and grow healthier grass. Antagonistic microorganisms such as fungi feed on nematodes. Too much organic matter should be avoided, as that can cause excessive turf growth that would be less drought and cold tolerant.
One of the best ways to prevent nematode damage is by increasing the grass' ability to tolerate nematode damage. If resodding or starting a new lawn, choose varieties of grass that is more resistant to nematodes. Bahia grass tends to be more tolerant of nematodes than some other common lawn grasses. Be aware of the many types of nematodes. For example, centipede grass is the only common lawn grass damaged by ring nematodes. If replanting in an area known to have had ring nematode infestation, avoid using centipede grass.