Nursery, Greenhouse, and Landscape News

Use of Entomopathogenic Nematodes with Selective and Short-residual Insecticides

Entomophagous nematodes are effective against pests that occupy moist habitats including soil, leaf mines, and stems. Pest managers can have plants with pests in both moist and dry habitats. For example, black vine weevil larvae could be feeding on the roots of a plant while caterpillars or aphids feed on leaves. Growers seeking to conserve local natural enemies may use insecticidal soap or a neem extract to kill the aphids, Bacillus thuringiensis (Bt) or neem to kill the caterpillar, and nematodes to kill the black vine weevil larvae. Procedures for nematode and pesticide applications can be at odds with one another. How growers mix or sequence the use of these pesticides with nematodes can greatly alter control effectiveness. Nematode applications should be watered into soil when applied against soil insects. Irrigating plants, however, can wash off short residual insecticides like Bt, neem, soap, or horticultural oil, rendering them useless. These insecticides should be put on after nematodes are applied to maximize their pesticidal activity. Unfortunately, however, this can greatly increase the labor involved during the application process. Recent studies indicate the entomophagous nematode species may survive being tank- mixed with commercial formulations of Bt, insecticidal soap, or neem (Margosan-O). Nematode infectivity of the mix is greatest when the soil was irrigated prior to application and if applied on the day it was made. Storage of the nematodes, Steinernema carpocapsae, and Heterorhabditis bacteriophora with pesticidal soap (M-Pede) kill both nematode species after a day in solution. Although nematodes in aerated mixes of pure Bt retained infectivity, after 4 days, they lost infectivity in commercial formulations of Bt (Javelin- 1 day, Biobit- 3 days). Heterorhabditis bacteriophora was more easily killed by the soap and the commercial Bt formulations. Three species of nematodes -- S. carpocapsae, S. feltiae, and S. glaseri -- survived and were infective when left in a tank for up to 15 days in solution with neem (Margosan-O). S. feltiae and S. carpocapsae, however were more adversely affected by neem.

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