A nematode soak is a method of biological pest control utilizing beneficial microscopic worms, known as entomopathogenic nematodes (EPNs), suspended in water. This approach is primarily employed in gardening, landscaping, and agriculture to manage soil-dwelling insect pests. By applying the nematodes in a liquid solution, they are delivered directly to the root zone where pest larvae reside. The success of a nematode soak relies on the precise preparation and application of the solution to maintain the viability of these living organisms.
Identifying the Beneficial Organisms
Nematodes are roundworms, and the beneficial types used for pest control are specifically entomopathogenic, meaning they are insect-parasitic. These microscopic organisms are entirely harmless to humans, pets, and plants, posing no risk to non-target organisms like birds or earthworms. The two most common genera used commercially are Steinernema and Heterorhabditis, which are chosen based on the target pest and the required soil temperature.
Beneficial nematodes work in a symbiotic relationship with specific bacteria. Once the nematode locates a host insect, often by sensing chemical signals in the soil, it enters through natural body openings like the mouth or spiracles. Inside the pest, the nematode releases its associated symbiotic bacteria. These bacteria multiply rapidly, producing toxins that quickly kill the host insect, usually within 24 to 48 hours. The nematodes then feed and reproduce within the dead host, and a new generation of infective juveniles emerges to search for more pests.
Preparing and Mixing the Solution
Proper preparation of the nematode soak solution is essential for ensuring a successful application, as these are living organisms. Upon arrival, nematodes should be stored in a refrigerator, ideally between 38°F and 42°F, and must never be allowed to freeze. The solution should be applied as soon as possible after purchase, since their energy reserves deplete over time, reducing their ability to seek out and infect pests.
When mixing, start with clean, cool water, avoiding heavily chlorinated sources, as chlorine can harm the nematodes. If using tap water, allowing it to sit for several hours helps dissipate the chlorine. The water temperature should be moderate, ideally between 50°F and 68°F, since extremely hot or cold water can damage the nematodes. The product, often supplied in a paste, is mixed into the water, and any fine filters (50 mesh or smaller) must be removed from application equipment to prevent clogging.
Continuous agitation is necessary during the mixing process, as nematodes are heavier than water and settle quickly to the bottom. Settling can cause them to suffocate or result in uneven distribution during application. Agitation can be maintained manually with a stirrer or automatically with a small submersible pump. The prepared solution should be applied immediately, ideally within one to two hours of mixing.
Application Techniques and Target Pests
A nematode soak delivers the active organisms directly to the soil or root zone, where many pest larvae are feeding. Application should be timed for the cooler parts of the day, such as early morning or evening, because nematodes are highly sensitive to ultraviolet light and desiccation. The target soil or growing medium must be pre-moistened, as nematodes require a film of water to swim and move in search of prey.
One primary application method is the soil drench, where the solution is applied to the soil surface to saturate the root zone. This technique targets soil-dwelling pests such as fungus gnat larvae, white grubs, and root weevils. For container plants, a drench may be applied until the solution begins to drain from the bottom, ensuring the nematodes reach the entire root ball.
After application, the treated area should be lightly watered again to help wash the nematodes deeper into the soil. The moisture level must then be maintained for several days to allow them to establish and actively hunt.
Another specialized technique is dipping or soaking, which is often used for bare-root plants, cuttings, or transplants before they are planted. Submerging the roots in the nematode solution provides immediate protection against early root-feeding pests. The choice of nematode species is specific to the pest; for instance, Steinernema feltiae is commonly used for fungus gnat larvae. The overall process is most successful when the application is preventative or aimed at low to moderate pest populations, focusing on the susceptible larval stages of the insects.