Insect and Mite Control on Woody Ornamentals and Herbaceous Perennials

Bulletin 504

Alternative Products
Their Selection and Use for Insect and Mite Control on Ornamentals

Entomopathogenic Nematodes

Nematodes are commonly called roundworms. They comprise a very large and diverse group which include general scavengers, predators, plant infesting and animal infesting species. A certain group of nematodes attack insects by entering the insect gut or body, regurgitating a lethal bacterium and reproducing in the insect cadaver. These are called entomopathogenic. These nematodes have a mobile, infective juvenile (the J3 stage) which is microscopic and can be sprayed through conventional equipment. These infective juveniles are quite resistant to many chemicals but they can not withstand rapid drying or prolonged contact with sunlight.

There are numerous species which belong to the genera Steinernema or Heterorhabditis. Both steinernemid and heterorhabditid nematodes have been found in native soils. However, many of the strains currently marketed and under development have come from foreign countries.

Up to the early 1980s, attempts to use these nematodes as biological controls were rarely successful. The nematodes are weakly persistent and rearing sufficient numbers to work was costly.

In the 1980s, several companies developed large scale rearing techniques, often using large scale fermentation technology. This allowed for the production of nematodes in sufficient quantity to be commercially useful.

Because the nematodes are considered animals rather than microbial agents, they are considered by the U.S. EPA to not require pesticide registration.

Mammalian Toxicity: Entomopathogenic nematodes are noninfective to mammals, birds, fish or other animals except certain insect groups. Some of the residues from nematode production or formulation materials may cause eye irritation, so eye protection during mixing may be in order. Field studies have also indicated that the nematodes rarely come into contact with beneficial insects and mites.

Uses: Since entomopathogenic nematodes are exempt from U.S. EPA registration, caution must be taken when evaluating supplier claims of efficacy. Current research indicates that the nematodes have been useful in reducing black vine weevil larval populations, especially in containerized plants. Other studies have indicated activity against certain borers (when the J3s are applied to borer holes or frass), leafminers and soil inhabiting pests.

The infective juveniles are applied at 1x10⁶ to 2x10⁹ J3s to the acre. Because they are living organisms, they must be applied so as not to expose them to direct sunlight for any length of time and they must be allowed to contact moist surfaces so as not to dry rapidly.

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