Turf-eating White Grubs Can Be Hard To Control

By for CAES News

Some of your lawn's worst enemies look like pudgy little pushovers. But they can be harder to kill than Rambo.

University of Georgia experts say white grubs, little C-shaped larvae with creamy white abdomens and brown heads, aren't all that tough. But they're mighty hard to reach.

"It's very difficult to deliver an insecticide to the target area," said Beverly Sparks, a UGA entomologist in Athens, Ga.

"Turf is a good filtration system," Sparks said. "But the same aspect that helps turf protect the groundwater makes it harder to protect the grass itself. For a product to be effective, you have to get it down through that turf 3 to 4 inches into the soil."

White grubs are the larvae of Japanese beetles, green June beetles, May and June beetles and chafers. Wilting or brown grass patches may be a sign that they're eating your lawn.

Many older products will kill white grubs. The best are granular forms of diazinon, chlorpyrifos (Dursban) and isofenphos (Oftanol). Trichlorfon products (Proxol or Dylox) are also registered for use on lawns.

Kris Braman, a UGA researcher in Griffin, Ga., said some newer products are promising. They may be safer for the environment, too.

"One product, Merit, has been on the market a couple of years now," Braman said. "It's a broad-spectrum systemic product that's effective at very low use rates. And it's less harmful to nontarget species."

Another product, Mach 2, is a growth regulator. "It interferes with the insects' ability to molt and grow," she said. "It's relatively less harmful to white grubs' natural enemies and beneficial insects."

Both new products zero in on the problem pest better than the older pesticides. "That's a trend I think is going to be true of all new products," Braman said.

If you're going to use either, though, don't wait to do it. "With older products we were concerned about having them out too early," Braman said. "But the newer products have different modes of action."

To get the best control, apply Merit while the adult beetles and eggs are present. "It's best to apply Merit two to four weeks after the peak flight of the parent beetles," she said.

The peak flight of Japanese beetles is easy enough to note. Look for less obvious beetles, such as May beetles or chafers, to be flying around lights at night.

"Mach 2 needs to go out earlier, too," Braman said. "But we seem to have a little more flexibility with it. It's generally most effective in late July and early August."

The older products may work better as white grubs get larger. They can still work well in late August and into September.

Whatever the product, the UGA experts say the key is to get it 3 to 4 inches into the soil. "To do that, you have to use a half-inch of irrigation," Braman said.

If you've had a problem with white grubs in the past, Sparks said, check turf for them in August and September. Cut three sides of a square foot of turf with a shovel. Then fold the sod flap back and look for grubs in the top 2 or 3 inches of soil and roots.

"If you find more than four, contact the county extension office," she said. "The county agent can help you identify the species you have."

Some species, she said, can damage turf with just four grubs per square foot. Others can have 10 to 20 per square foot and still not damage turf.

Braman said new biological products, including some soil nematodes and Bacillus thuringiensis products, may soon help control white grubs.

"These new products provide different modes of action," she said. "And they help us avoid resistance problems in white grubs."

Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.