Not all insects damaging turf are visible from surface scouting. White grubs, the larvae of several species of May or June beetles, and billbug larvae can be very destructive to turf without ever being seen as they feed on grass roots about an inch deep into the soil.
White grubs, when fully grown, are whitish or grayish in color, about one and a half inches long, with brownish heads, three pairs of legs, and characteristically rest in a C-shaped position. Billbug larvae are about one-third this size and are legless. Under the most severe infestations the turf can be literally lifted by hand from the soil as most all roots have been completely eaten. Often a tale-tale sign of grub damage is digging by skunks, raccoons, armadillos, and moles as they search for the grubs.
Now is a good time to scout for grub damage as the larvae are still small making them easier to control and there is still time for the turf to recover from their injury before winter. To determine if you have a grub problem, cut several one foot square samples of turf from your lawn to a depth of two inches into the soi. Then, crumble the soil from the turf examining for active grubs. If you find an average of three to five grubs per square foot, then you should treat with an appropriate insecticide.
When treating with insecticides, water dry soil before applying and again after treating to ensure the insecticide moves in contact with the grubs. Extension Publication #2331, Control of Insect Pests In and Around the Home Lawn, is an excellent resource for more information on these and other lawn insect pests. You can obtain a copy by downloading here or your local extension office.
Published July 11, 2005
Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. firstname.lastname@example.org