Beneficial nematodes are microscopic, non-segmented roundworms naturally found in soil environments. These organisms, termed entomopathogenic nematodes, are used as biological pest control in gardening and agriculture. They actively seek out and infect insect pest larvae, releasing a symbiotic bacterium that kills the host. Importantly, these natural pest controllers are non-toxic and pose no threat to humans, pets, or beneficial insects like honeybees and earthworms. Their use offers an environmentally conscious method for managing pest populations without introducing chemical residues.
Identifying the Right Nematode Species
Selecting the correct nematode species is important for successful pest control, as different varieties target specific insects. The choice depends entirely on the specific pest you are trying to manage. Two of the most common and commercially available species are Steinernema feltiae and Heterorhabditis bacteriophora.
Steinernema feltiae (S. feltiae) is recommended for controlling pests that live in the top few inches of the soil or in cooler environments. This species is effective against fungus gnat larvae, common houseplant and greenhouse pests, and the pupae of western flower thrips. Because S. feltiae remains active in soil temperatures as low as 50°F (10°C), it is suitable for earlier spring or late fall applications.
In contrast, Heterorhabditis bacteriophora (H. bacteriophora) is the preferred choice for larger, more deeply buried pests, such as various species of white grubs and weevil larvae, including the Japanese beetle grub. This species actively moves deeper into the soil profile to find hosts. H. bacteriophora performs best in warmer soils, requiring temperatures above 60°F (16°C) for maximum efficacy.
Retail Options and Purchasing Considerations
When purchasing beneficial nematodes, you will encounter several retail channels, each with varying implications for product quality and viability. Specialized online suppliers of biological controls are often the most reliable source, as they focus on maintaining the cold chain and guaranteeing live delivery. These vendors typically ship the nematodes quickly in insulated packaging to ensure the organisms remain viable upon arrival.
Large national garden centers and retail stores also carry nematodes, but the quality can be inconsistent due to storage conditions that may not be optimized for live organisms. Nematodes are shipped and stored as dormant infective juveniles, and exposure to high temperatures or prolonged shelf life significantly reduces their effectiveness. Always check for a production or expiration date on the packaging to ensure the product is relatively fresh.
Nematodes are commonly sold on an inert carrier material, such as a water-soluble powder or a sponge/gel pack. The powder forms are often used for bulk applications, while the sponge or gel packs are intended for smaller, residential use. The most crucial consideration is the viability guarantee from the seller, which confirms the nematodes are alive and capable of infecting pests. Reliable suppliers often provide a guarantee that covers the live count and condition upon delivery.
Handling, Storage, and Application
Once beneficial nematodes are purchased, proper handling and immediate use are necessary to maintain their viability. Nematodes should be stored in a refrigerator between 35°F and 45°F (2°C and 7°C) until application. Avoid freezing the product, as this will kill the organisms.
For application, the nematodes must be mixed with water according to the package directions, ensuring continuous agitation to prevent settling. If possible, use non-chlorinated water, such as rainwater, or allow tap water to sit for a few hours to let the chlorine dissipate, as high chlorine levels can negatively impact the nematodes. The ideal time for application is during the early morning or evening hours, or on a heavily overcast day.
Direct sunlight must be avoided during application because ultraviolet (UV) light rapidly kills the nematodes. Before and after applying the solution, the soil should be thoroughly pre-watered and kept moist for at least the first week. This moisture is important because the nematodes require a film of water to navigate through the soil pores to reach the pest larvae.