Grubs, the larval stage of various beetles like Japanese beetles and masked chafers, are common lawn pests that feed on grass roots, causing brown patches and turf damage. Entomopathogenic nematodes, which are microscopic, naturally occurring roundworms, offer an environmentally sound biological control option for managing these soil-dwelling pests. These beneficial organisms actively seek out and eliminate grubs, providing a targeted solution for lawn health.
Selecting the Correct Nematode Species
Choosing the correct species is necessary for successful control, as not all beneficial nematodes are equally effective against lawn grubs. The most effective choice for white grub control is Heterorhabditis bacteriophora (Hb). This species is known as a “cruiser” because it actively hunts and moves throughout the soil profile to find its grub host.
H. bacteriophora targets sedentary grubs deeper within the soil, sometimes burrowing down to seven inches. Once it finds a grub, the nematode enters through a natural opening and releases a symbiotic bacterium, usually from the genus Photorhabdus. This bacteria causes a fatal infection, killing the grub within 24 to 48 hours.
This species should be distinguished from others, such as Steinernema feltiae (Sf), which targets fungus gnats and thrips, or Steinernema carpocapsae (Sc), which targets surface-dwelling pests. H. bacteriophora is superior for the deep-dwelling white grubs. Purchasing a combination product that includes H. bacteriophora ensures the best coverage.
Sourcing and Purchasing Options
The quality and viability of the nematodes are paramount, as they are living organisms that must be handled carefully. The most reliable source for purchasing nematodes is online specialty suppliers who focus on biological pest control. These vendors typically have a high turnover of stock and are experienced in shipping the organisms in temperature-controlled packaging.
When ordering online, check the vendor’s shipping methods; the nematodes should arrive cooled, often on a damp sponge, in a gel, or in a powdered clay mixture. Upon arrival, store the package immediately in a refrigerator, but not frozen, until application. The product should be applied as soon as possible, and the viability and shelf life are limited, sometimes lasting only a couple of weeks for larger quantities.
Local garden centers and nurseries are another option and may carry refrigerated nematode packages, but it is important to confirm the product’s expiration date or check the refrigeration status. A decaying smell upon opening the package suggests the nematodes have perished. Big box stores may also stock nematode products, but their handling and storage conditions can be less consistent.
The required quantity is calculated based on the area to be treated, with application rates ranging from 5 million to 25 million infective juveniles per 1,250 to 5,000 square feet. Purchase only what is needed for immediate application, as storing them for long periods can reduce their effectiveness. Always check the species listed on the packaging to verify that it includes Heterorhabditis bacteriophora for maximum grub control.
Critical Timing and Application Instructions
Successful grub control depends on applying the nematodes when the grubs are small, actively feeding, and close to the soil surface. The best time for application is late summer to early fall, often between late August and mid-September. This timing targets the new generation of grubs when they are in their most vulnerable young stages. Spring applications, usually around early May, are a secondary option, but the grubs are larger and harder to eliminate.
The soil must be moist before and after application to allow the nematodes to move effectively. Nematodes require a minimum soil temperature of 50°F to 55°F to be active, with an optimal range being 68°F to 86°F. Application should occur during the cooler parts of the day, such as early morning or late evening, or on an overcast or rainy day.
Nematodes are sensitive to ultraviolet (UV) light, which can kill them. They are mixed with water and applied using a hose-end sprayer, watering can, or specialized equipment. Continuous agitation of the mixture is necessary to prevent the nematodes from sinking. Immediately following application, the treated area should be watered thoroughly to wash the nematodes into the soil where the grubs are located. Keeping the soil moist for the next two weeks is important for the nematodes to establish and seek out their hosts.