Dealing with Grubs in Lawns – Treat in Late June
White grubs, the larval stage of Japanese or June beetles, damage and kill lawns by eating grass roots. Infected lawns show brown, irregularly shaped patches that appear in summer and early fall. Severely damaged areas can be picked up whole, as the grass no longer has roots to hold it into the soil.
More About Grubs
According to Michael Merchant, Texas A&M extension service entomologist, all of the common warm season grasses – Bermuda grass, zoysia, St. Augustine and buffalo grass – are vulnerable to attacks by white grubs. Infestations some years are worse than others are. Neil Sperry, author of “The Complete Guide to Texas Gardening” (Taylor publishing, 1991) describes these damaging grubs as about one-half inch long, curled into crescent shape with white bodies and brown heads.
In May or June, the adult beetles emerge from the soil usually after heavy rains or irrigation in search of a mate. Light attracts males and they may be found under porch lights or around lighted windows. The active period for the beetles lasts several weeks in May and June before the female digs a 2 to 5 inch hole into the turf and lays between 30 and 40 eggs. The eggs hatch in approximately two weeks.
Grubs pass through three larval life-stages. The first two life stages last about three weeks each followed by the third stage that continues until the adult emerges the following spring. The third stage does the majority of lawn damage because the hungry grubs continue eating grass roots until cold weather when grubs are dormant.
Treating Grubs in Lawns
More than four or five grubs per square foot of lawn require treatment. Confirm that the lawn has grubs by pulling up a small section of grass and checking for grubs. The irregular patches and lack of vigorous growth caused by grub damage looks similar to brown patch in St. Augustine. However, the treatment for white grubs is different.
If a lawn has grubs, treating at the right time is essential. In the past, diazinon and Dursban were recommended chemical treatments applied in mid- to late July. However, these products are no longer available to home gardeners after the Environmental Protection Agency remove chlorpyrifos from the market. Today, treatment today for lawn grubs uses products containing Imidacloprid or halofenozide.
Check product labels and apply according to package directions. Imidacloprid controls all larval stages whereas halofenozide only kills grubs in stages one and two of their life cycle. Because of the way these chemicals control grubs, late June and early July are the best time to apply them.
After treating a lawn for grubs, water the grass thoroughly to get the chemical down to the root zone. If a lawn has more than ½ an inch of thatch buildup, remove or de-thatch before applying chemicals.