Beneficial Bugs Known as Parasitic Nematodes

Organic gardeners unfamiliar with parasitic nematodes should become acquainted with this humble species, which includes more than 20,000 microscopic worms that dwell in the soil. Although many nematode species are poorly understood, several commercially available types of beneficial nematodes can hone in on garden pests without affecting soil health, pets, or wildlife.

Understanding Nematodes

Entomologists often describe the simplistic nematode as a tube within a tube, which describes the digestive tract that extends the length of the nematode’s body. Parasitic nematodes travel for short distances through moist soil searching for host insects, which are specific for each species of nematode.

Upon encountering a host, a juvenile nematode pierces the insect or enters through a natural orifice to begin feeding. The host insect dies within a few days, and when the dead insect ruptures, thousands of new parasitic nematodes may be released into the soil.

Beneficial Nematode Types

Parasitic nematodes are so benign to humans and animals that there is no restriction on their use in gardens or farms. Soil dwelling pests such as grubs are more susceptible to parasitic nematode control than insects like grasshoppers. The organic gardener must first determine what insect is plaguing the garden to buy nematodes that will target the pest.

Steinernema is a widely available parasitic nematode. Gardeners concerned with cultivating an organic lawn can use S. carpocapsae to control turf pests such as sod webworms and billbug larvae. Greenhouse growers may use S. feltiae to control fungus gnats.

Heterorhabditis is not as commonly available as Steinernema, but it’s worth seeking out for gardeners concerned with the ubiquitous white grub. Organic gardeners raising citrus should also explore this species for its ability to control citrus root weevils.

Using Beneficial Nematodes

Gardeners working with beneficial parasitic nematodes must remember that they are working with live insects, which are vulnerable to environmental conditions and temperature extremes. Commercially available nematodes have a short shelf life, so gardeners should not order them until they detect the target pest. If application is delayed, store nematodes in the refrigerator.

Beneficial nematodes often arrive packaged in the form of an impregnated sponge. Gardeners must keep the sponge moist at all times, as dry conditions cause death quickly in nematodes. Application of parasitic nematodes to the garden soil is usually accomplished with the help of a compression or tank sprayer.

Apply the nematodes when rain is in the forecast, to help the nematodes navigate through the soil to their host. If conditions remain dry, use a sprinkler to soak the soil deeply, so pests can’t travel to the safety of a dry zone in the soil.

Sources:

University of Nebraska-Lincoln’s Nematology Department

Colorado State University Extension