Nursery, Greenhouse, and Landscape News

Water and Nematodes: Two Tools for Managing White Grubs in Turf

Homeowners, landscapers, and golf course superintendents wrestling with the problems of white grubs in turf should be glad to know that biological control alternatives are becoming more feasible with each passing season. Every summer, white grubs, the larvae of scarab beetles, devastate turfgrass by consuming its root system, leaving lawns high and dry in the afternoon sun. One of the more obvious strategies for dealing with grubs is to add water to lawns. This can allow the turfgrass to get enough water even though the roots are injured. The specific density of grubs that can be tolerated by turf will vary with the turfgrass species and the species of grubs that is present. Acceptable densities for grubs on vigorous irrigated turf range from 6 to 20 per square feet. Refraining from insecticide use in areas of turf where grub densities are below the acceptable density can increase the opportunities for native natural enemies of grubs to reduce pest numbers. Increasing the tolerable threshold for grubs through irrigation is not without its own special set of problems. Vertebrate grub predators can still dig up apparently healthy grub infested turf and destroy it. Clearly, there is still a need for grub control.

Entomophagous nematodes can be mixed into a spray tank and be very effective against certain grubs under the correct conditions. As with using nematodes against bagworms, the trick is to get them through the thatch to the grubs before they dry out. Recent work conducted on two white grubs, Japanese beetle and the oriental beetle, indicate that irrigation can greatly improve the chances of getting effective control with the nematode Steinernema glaseri. Nematodes gave good control when applied in mid- to late-August in 5 gallons of water at a rate of about 23 million per 1000 square feet, followed immediately by 1/4 to 1/2" irrigation. Control was even better when 5 times as many nematodes were applied in 5 gallons of water prior to irrigation.

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