ANNUAL WHITE GRUBS ARE EARLY THIS YEAR!
Tagged as:
Fredric Miller, Ph.D.
University of Illinois
Countryside Extension Center
Countryside, IL 60525
Peak emergence of adult southern masked chafers, the adult stage of the annual white grub, occurred on July 7th in northern Illinois, about seven days early this year. Usually they emerge in northern Illinois around the second week of July.
The adult beetles are about ¼ inch long and tan colored. This beetle is not the same as the May/June ("bug") beetle that emerges in late May and early June. Adult female southern masked chafers lay eggs in the moist soil and the eggs hatch into "grubs" which feed on the roots of turfgrass. The grubs will feed until late fall and then overwinter. There is one generation per year. In cases of severe feeding, the sod may be "loose" and pulled up with minimum effort much like freshly laid sod. The grubs can be easily seen under the loose sod and on the soil surface. The grubs are small initially but will grow to be about ½ inch long with a white body and brown head. They have a typical "C" shape. Feeding damage by the grubs will result in brown, irregular-shaped patches. Be sure to confirm that grubs are responsible for the damage as many other turfgrass diseases and cultural problems may mimic grub damage.
When and should you treat for grubs? Since the adults emerged earlier this year, grub damage may start occurring by late July instead of the more typical early to mid August. Weather (soil temperatures and rainfall) will have a tremendous impact on grub damage and timing for insecticidal treatments. Since it has been rather dry the last several weeks, grub populations may be more concentrated in irrigated areas. Areas that did not receive rainfall during egg laying may have lower populations because the adult female beetles like to lay their eggs in moist soil. If this hot, dry spell continues, with little or no rainfall, egg and grub mortality may be significant. This could also significantly affect later grub populations and subsequent turf damage.
In order to effectively prevent grub damage, check first to make sure grubs are present. Pull the sod back and examine the soil surface. If grubs are present, they will be readily visible. Do not assume that every brown patch is due to grub feeding. If grub populations exceed 10-12 per square foot, then treatment is usually warranted. Sample throughout the affected area and get a good idea as to the "big picture". Grub populations can vary greatly from location to location. If treatment is warranted, apply a soil insecticide. There are several different products available. Be sure to read and follow the label directions. Be sure to thoroughly water the insecticide into the soil during application to insure that the grubs come in contact with the insecticide. Usually a drenching equivalent of ½ to ¾ inch of moisture should be adequate. One application is all that is needed. It will usually take 10 - 14 days for the grubs to die, but they cease feeding within 24 hours. Generally grass roots will regenerate and affected areas will recover.
To review, thoroughly inspect the affected area, make sure grubs are present, and then treat only if grub populations exceed treatment thresholds. Grubs are easily managed if you follow these basic steps.