By Dan Rahn
University of Georgia
"It's very hard to deliver an insecticide to the target area," said Kris Braman, an entomologist with the University of Georgia College of Agricultural and Environmental Sciences on the Griffin, Ga., campus.
"Turf is a good filtration system," Braman said. "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. With creamy white abdomens and brown heads, they look harmless. But they're not. Wilting or brown grass patches may be a sign that they're eating your lawn.
The right stuffBraman said many older pesticides are no longer available for white grubs. "Trichlorfon (Bayer Advanced) and carbaryl (Sevin SL) are among the only products that will provide curative control of large grubs that are registered for use on lawns," she said.
Newer products can be effective, too, and may be safer for the environment.
"One product, imidacloprid, has been on the market for several 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."
Imidacoprid is also sold under the Bayer Advanced label, she said. Be sure and check the label for the appropriate product.
Say 'when'"The challenge is to apply the product at the correct time, because it only works on small grubs," she said. In Georgia, the grubs are usually still small during July and early August.
Another product, halofenozide, is a growth regulator. "It interferes with the insects' ability to molt and grow," Braman said. "It's relatively less harmful to white grubs' natural enemies and beneficial insects. It also needs to be applied to target the young grubs."
So, whatever pesticide you use, don't wait to do it. To get the best control, apply imidacloprid while the adult beetles and eggs are present. "It's best to apply imidacloprid 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.
"Halofenozide 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 July and early August."
Whatever the product, 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.
Which ones?If you've had a problem with white grubs in the past, she said, check your lawn 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 UGA Cooperative 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.)