Nursery, Greenhouse, and Landscape News

Don't Destroy White Grub Natural Enemies with Early Season Applications of Soil Insecticides in Turf

The turf habitat is surprisingly rich in natural enemies of turf pests. In this Kentucky study, ants were by far the most abundant predators, accounting for more than half the predators found, followed by spiders, rove beetles, ground beetles, tiger and hister beetles. These predators can have a significant impact on turfgrass pests. Up to 74% of Japanese beetle eggs, and 53% of fall armyworm pupae placed in pesticide free plots of Kentucky bluegrass were removed by natural enemies in 48 hours. Soil applications of carbaryl, cyfluthrin, and isazofos in 10 m X 10 m plots greatly reduced the populations of most of these natural enemies for 6 to 10 weeks. Ant populations were suppressed even longer. Use of soil insecticides in early summer for billbugs, chinch bugs, or sod webworms has the potential to increase problems with white grubs by killing predators' eggs and young larvae. When the three soil insecticides were applied in mid-June, predation on Japanese beetle eggs placed in soil was reduced by more than half in the isazofos and carbaryl plots. By the end of the season, naturally occurring Japanese beetle grub densities was highest in isazofos treated plots. Turf managers seeking to conserve natural enemies of white grubs should use selective pesticides such as Bacillus thuringiensis when possible for sod webworm, and restrict pesticide applications for early season pests to areas where problems occur. Applications of soil insecticides for areas affected by white grubs should not be applied before eggs hatch. This can minimize the impact of the pesticide application on natural enemies by giving them a chance to feed on grubs, and providing them with safe havens in the turf.

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