Organic and biological means of controlling garden pests can reduce or eliminate the high costs and health risks involved with chemical alternatives. St. Augustine, a warm-season grass grown in southern United States, is susceptible to many types of soil-borne pests that reduce its appearance and damage its health. Beneficial nematodes are microscopes roundworms that feed on lawn-damaging pests, killing populations between 24 to 48 hours without harming the soil.
Beneficial nematodes have many advantages over chemical pesticides and insecticides. Because chemical pesticides are non-specific, they kill both harmful and beneficial garden insects, thus disrupting microbial activity. Beneficial nematodes target harmful soil-borne insects without killing parasitic wasps, ladybugs and lacewing bugs. While studies show many insects develop immunity against frequent applications of a particular pesticide, no cases exist to prove insect resistance to beneficial nematodes. Unlike pesticides that cause skin and eye irritation, types of cancer and reproductive problems in humans if mishandled, ingested or overexposed to, nematodes are safe for use in gardens frequented by children and pets because they do not harm vertebrates.
For best results, release the beneficial nematodes over the St. Augustine lawn when soil temperature lies between 50 and 90 degrees Fahrenheit, and preferably in the evening. Water the area before and after application as delicate nematodes dry out or die easily in warm soils or exposure to sunlight.
Not one but several different types of nematodes exist, requiring the gardener to select one that specifically preys on the existing lawn insect. For instance, use Steinernema capocapsae against cutworms, sod webworms, chinch bugs, armyworms, wood borers, billbugs and girdlers in St. Augustine lawns. According to the University of Connecticut Integrated Pest Management Program, grubs, the larvae of different beetles, feed on and destroy St. Augustine grass roots fall prey to Steinernema glaseri. Steinernema scapterisci and Steinernema riobrave prey on mole crickets while Steinernema feltiaeis kills fungus gnats. According to the University of Florida Extension, heterorhabditis bacteriophora (Hb) controls lawn-damaging scarab beetles and billbugs.
Some types of beneficial nematodes can be stored at room temperature for up to three months or in a refrigerator for up to six months. Storage instructions are specified on the package containing nematode culture.
The Washington State University Cooperative Extension suggests ordering fresh nematode culture two to three days before application to ensure higher survival rates, as opposed to storing them for months prior to use. Alive, wriggling nematodes feature an S or J shape when inspected under a microscope, while dead ones are straight and listless.
According to the University of Florida Extension, beneficial nematodes decline and die two to three weeks after they feed on their prey. If higher concentrations are used, they kill their prey and die soon after, thus requiring more applications in case new insect problems arise, increasing excess costs. For best results, use sparing populations of nematodes that continually kill existing and developing insects throughout the lawn.