Beneficial nematodes can be an organic gardener's best friend. Also called "parasitic" or "predatory" nematodes, these microscopic, non-segmented round worms seek out soil-dwelling insects and larvae and use them in their reproductive cycles -- a process that kills the insect host within 24 to 48 hours. Pests that fall prey to nematodes include species of weevils, borers, beetles, ants, fleas, flies, snails, grubs, termites and worms. Beneficial nematodes can occur naturally in soil but in most cases they must be purchased and added under optimum conditions. They won't survive dry or cool conditions and will need to be reintroduced if the insect problem recurs next season.
Identify the insect that is causing the problem in your lawn and garden. This will help you select the correct nematode species.
Purchase the nematodes from a mail order supplier or garden center. Nematodes are sensitive to environmental conditions, so going directly to the manufacturer may help ensure you receive enough live nematodes to solve your pest problem. Check the proportion of live nematodes in your order by viewing a small amount of the material you received under a microscope or hand lens. Use the nematodes as soon after receiving them as possible.
Check the weather for optimal conditions. This includes moderate air temperatures and high humidity --morning and evening are best. Soil temperature should be between 60 and 90 degrees.
Water the garden or lawn area where you will apply the nematodes, using a garden hose.
Apply the nematodes according to manufacturer directions. This usually entails mixing the concentrated nematodes with water and applying to the soil with a spray bottle or watering can. Use non-chlorinated water or allow the chlorine to disperse from tap water by letting the water sit out overnight. Once you've added the nematodes, use the water within two hours. Gently agitate the nematode solution during application to ensure an even spread.
Water the area thoroughly, using a sprinkler, to help the nematodes quickly enter the soil. Do this immediately after application.
Add more nematodes, following the instructions above, if you don't see a decline in the number of pests within two to three weeks. Since nematodes attack the larval stage of many insects, they will affect only the next generation of the insect pest. Keep the length of the life cycle of your particular pest in mind when gauging the success of nematode application.