By Dan Rahn
University of Georgia
White grubs don't look so tough. But the pudgy little C-shaped
larvae can be like tiny terrorists, attacking your lawn while
staying downright hard to get to.
"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 stuff
Braman 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.) |
