Predatory nematodes commercially packaged are a very safe biological insecticide containing inert material and millions of the beneficial nematodes. Unlike the harmful rootknot nematodes which attack plants, beneficial or predatory nematodes only attack soil-dwelling insects. Nematodes are microscopic, non-segmented eel-like worms one-tenth to one-hundred-twenty-fifth of an inch in length. It is a natural product that will control a broad spectrum of soil dwelling grubs and larvae of pest insects. These naturally occurring organisms, sold by a number of different companies, are applied to the soil, then seek out and move to the target insects to kill them. Predatory nematodes will attack all the larvae and grubs found in the soil. These will usually be from the eggs of beetles and weevils.
When released into the soil, beneficial nematodes are attracted to the heat and carbon dioxide emitted by healthy larvae of destructive grubs. These nematodes enter the host through natural body openings and release a toxin that is fatal only to the grub. Death occurs within 24 to 48 hours. The nematode then reproduces, and its many progeny leave the host's body and begin search actively for other susceptible insect pest larvae. Beneficial or predatory nematodes can live in the soil and kill insects for many weeks, depending on the soil's moisture and temperature. The soil should not be dry and the best results occur when the temperature of the soil is above 60 degrees.
There are at least two strains or varieties of beneficial nematode on the market -- Heterorhabditis heliothidis (Hh) and Neoaplectana carpocapsae (Nc). Both are effective grub controls if purchased from a reputable source.
No insect has developed resistance to parasitic nematodes, or is any likely to do so. The reason is simple. Nematodes kill every insect they invade; no host insect can survive to start a resistant strain.
Effectiveness of Predatory Nematodes
Effectiveness of a pesticide relates to how thoroughly it kills or controls a pest insect. In most cases in the home landscape, an insecticide is effective if it controls 60% to 80% of the pests in question. Predatory nematode products, when applied properly should achieve 60% to 80% control within two weeks. As with all pesticides, the relative concentration of predatory nematodes in a spray solution is very important to its effectiveness. Consequently, if you are using a concentrated form that needs to be diluted, you should always read the label on the bottle before mixing this product with water.