Head Off Lawn Grubs in July

Salina, Kansas (July 8, 2010)--Ancient Egyptians thought their black, dung-rolling scarab beetles were sacred. But, today´s Kansans are more likely to think their state´s 200 scarab species are pests.

The scarabs known as May (or June) beetles can be particularly irritating when they congregate around outdoor lights during late spring and early summer. The scarabs most Kansans worry about, however, are the species known as masked chafers, which emerge as egg- laying adults in early to mid summer.

Masked chafer eggs soon produce the C-shaped and mostly white grubs found in the soil of every Kansas landscape. These larvae grow through summer, eat increasing amounts and become the state´s No. 1 lawn pest, said Chip Miller, horticulturist with Kansas State University Research and Extension.

"Timing is critical to their control - unless, of course, you happen to spade or till one up and then smash it. Lawn owners who apply grub preventer in April are much too early. Those who wait to see if they´ve got damage in September or October are much too late, although they may need to apply a rescue treatment then. In most years, the first half of July is the ideal time to take precautions," Miller said.

Of course, one problem with this approach is that the grubs live underground, eating such moist organic materials as turf roots. And, their unseen populations don´t reach damaging levels every year. In fact, some lawns never have K-State´s suggested minimum for taking action: 8-10 grubs per square foot.

"The common sense approach," Miller said, "is to limit preventer to areas with a history of problems."

He no longer recommends the traditional preventer products with carbaryl, permethrin or trichlorfon as the active ingredient. Their success depends on when the adult beetles take their annual mating flight.

Instead, Miller advises following the label directions exactly on products that contain either halofenozide (e.g., MACH 2, Kill-A-Bug Granules) or imidacloprid (Merit, GRUBEX, Long-Season Grub Control). They remain active longer. Once completely dry, though, they are safe around humans and pets.

The best way to apply granular products evenly is with a gravity-type (not broadcast) spreader, he said. When mixed with water, liquid products may require applications that equal 15 to 20 gallons per 1,000 feet of lawn. So, a hose-end sprayer can be the easiest way to deliver the label-recommended volume.

"Even though you apply granules on a dry lawn, both granules and sprays require you to follow up with one or more irrigations - each about 1 inch of water. The label will say how much to apply, and it´ll be essential," Miller said. "Liquid sprays can penetrate better if you also pre-water a quarter-inch or so."

K-State´s in-depth factsheet about white grubs, their damage and controls is available at any Kansas county or district Extension office or on the Web at www.ksre.ksu.edu/library/entml2/mf2635.pdf.

Contact:

Kathleen W. Ward
K-State Research and Extension
kward@ksu.edu