White Grubs in the Lawn
The white grubs that are damaging to Iowa lawns are called annual white grubs because they live for only one year. They live in the soil and feed on grass roots during late summer. Symptoms of grub damage include irregular patches of wilted, tan or dead turf. Sod can be pulled back easily, like a carpet, since the roots have been consumed by the grubs.
Not all lawns are infested with damaging white grub population every year. Check for grubs in late July and early August. Cut square foot sections of lawn in several locations of your yard. Search for small, white c©shaped grubs. Tamp sod back in place and water well to reestablish the sod.
An average of 10 or more grubs per square foot is justification for control. Decide if you can tolerate some grub damage. Lawns that are not drought stressed may tolerate higher grub populations.
The time to treat for white grubs is early August. Small, newly hatched grubs are more vulnerable to insecticides. Treatments made in spring and late fall are not recommended.
Insecticides available for grub control include diazinon, Sevin, Dylox, and Oftanol. It is very important to irrigate the lawn with 1/2 to 1 inch of water after treatment. It may take some insecticides a few weeks to destroy the insects.
Before using any insecticide, please read the entire label carefully. Directions for appropriate rate, storage and disposal, first aid, and recommended protective clothing and gloves are important.
This project has been funded by the Iowa Department of Agriculture and Land Stewardship through a grant from the U.S. Environmental Protection Agency.
Prepared by David D. Minner, extension turfgrass specialist and Donald R. Lewis, extension urban entomologist.