Beneficial nematodes offer a biological method for controlling various garden and lawn pests without synthetic chemicals. These microscopic, non-segmented roundworms are insect-parasitic nematodes that occur naturally in soils worldwide. Applied as a living agent, they target the larval stages of insects dwelling beneath the soil surface. Once applied, these organisms seek out susceptible hosts, enter the body through natural openings, and release symbiotic bacteria that kill the pest within one to two days. This action provides an effective approach to managing pest populations.
Selection and Preparation
Selecting the correct nematode species is the first step toward effective pest management, as different species target different insects. For instance, Steinernema feltiae is typically recommended for controlling fungus gnats and thrips pupae, which are common greenhouse and indoor pests. Conversely, species like Heterorhabditis bacteriophora are often used against larger, soil-dwelling pests such as white grubs, Japanese beetles, and black vine weevils. It is important to know the specific pest causing damage before choosing a product to ensure the nematode’s hunting strategy aligns with the pest’s location.
Upon receiving the shipment, nematodes must be stored properly to maintain viability. They should be immediately placed in a refrigerator, ideally at a temperature range of 35°F to 43°F, until ready for use. Freezing must be avoided, as extreme cold will kill them. Before mixing, allow the nematodes to warm up for about 30 minutes at room temperature to prevent temperature shock when introduced to the application water.
Preparation involves mixing the nematode-containing carrier material with clean, cool water that does not contain high levels of chlorine or fertilizer. The water temperature should remain below 95°F, as excessive heat can deplete the nematodes’ energy reserves. Thoroughly hydrate the carrier material and ensure the nematodes are fully dispersed in the solution. The resulting suspension should be gently agitated before and during application to prevent settling, which can lead to uneven distribution.
The Application Process
Beneficial nematodes can be applied using standard gardening equipment, including watering cans, pump sprayers, or hose-end sprayers, but these tools require minor adjustments. A crucial modification involves removing all fine filters or screens, particularly those finer than 50 mesh, from the spray equipment to allow the nematodes to pass through unimpeded. Failure to remove these screens can trap or physically damage the organisms, significantly reducing the treatment’s effectiveness.
When using a pump sprayer, the pressure should be kept below 300 psi to avoid physical harm to the delicate nematode bodies. Throughout the entire application, the solution must be kept continuously agitated, as the nematodes naturally settle quickly in water. This constant movement, which can be maintained manually or with a small submersible pump, ensures a uniform density of nematodes is applied across the entire treatment area.
The application delivers the nematodes directly into the top layer of the soil where the target pests reside. The suspension should be evenly distributed over the specified treatment area, such as the lawn, garden bed, or potting mix. Immediately following the application, the treated area must be lightly watered to wash any remaining nematodes off the foliage and into the soil. This irrigation is necessary because nematodes are susceptible to desiccation and cannot survive long on the soil surface.
Optimal Timing and Conditions
The success of a nematode application is highly dependent on favorable environmental conditions, particularly concerning temperature and moisture. Nematodes are sensitive to heat, and while the acceptable range is wide, typically between 42°F and 95°F, the ideal soil temperature for activity is often between 60°F and 70°F for many species. Applying the organisms when soil temperatures are too low or too high will dramatically reduce their ability to seek out and infect host insects.
Moisture is perhaps the most important factor, as nematodes require a film of water to move through the soil and locate their prey. The soil should be thoroughly watered before the application to provide this necessary medium for mobility. Following the treatment, the soil must be kept consistently moist for at least a week to ensure the nematodes can actively hunt and establish themselves in the environment.
Nematodes are also extremely vulnerable to ultraviolet (UV) light, which can damage their cellular structure and lead to rapid death if exposed. For this reason, the application must be timed to coincide with low light conditions, such as during the evening or on a heavily overcast day. Applying the suspension in the evening allows the nematodes to quickly penetrate the soil surface before the sun’s UV rays or the heat of the day can cause harm.