While the pretty part of spring is bursting into color, a
much less seemly part is
boring into many of the trees Georgians value, say University
of Georgia experts.

“Much of our woody plants have endured considerable
stress during the past 12
months,” said Kris Braman, an entomologist with the UGA
College of Agricultural and
Environmental Sciences. “They’ve had a year of drought,
floods, wind and ice
breakage. Now they’re particularly attractive to
borers.”

Asian Ambrosia
Beetles

Photo: Will Hudson

Telltale ‘toothpicks’ are a sure sign Asian ambrosia beetles have attacked this crape myrtle

For nursery growers, one of the meanest borers is the Asian
ambrosia beetle. This tiny
pest bores holes in the 1- to 2-inch stems of shrubs and trees
in early spring. The
severity of their attack has varied from year to year.

“They’re going to be a hot topic in the next two to
three weeks,” Braman
said.

Will Hudson, a CAES entomologist in Tifton, Ga., said it’s
usually easy to tell if
ambrosia beetles are attacking. Symptoms, he said, include:

• Sudden wilting of new foliage as the plants are leafing
  out.
• Sap running from small holes in the stems.
• A dead giveaway: toothpicks of sawdust protruding from
  the holes.

Beetles Attack Many
Plants

Asian ambrosia beetles usually show up in early to
mid-March. “They can invade
many species of otherwise healthy trees and shrubs,”
Hudson said. “In past
years, we’ve seen them on ornamental cherry, crape myrtle,
goldenrain tree, redbud,
hickory and Japanese maple.”

They may strike elm, oak, Bradford pear, apple and other
trees, too. “They’ll
attack almost any broadleaf tree or shrub of the right
size,” Hudson said.

Once the beetle is in the tree, it’s hard to kill, he said.
The most effective way to
limit losses has been to spray susceptible plants with
pyrethroid insecticides every 10 to
14 days as the spring flush is developing.

Timing
Important

Because timing is so important, CAES Extension Service
experts monitor traps around the
state to detect the first attacking beetles. County agents then
alert nursery growers.

“So far, only the souther tier of counties has seen any
significant
activity,” Hudson said.

Permethrin effectively protected susceptible plants in
screening trials. “Other
pyrethroid materials have been used with good results,
too,” he said.

Chemical treatment is practical only for nurseries. “In
most landscape
situations,” Hudson said, “there is little to do
except keep your plants as
healthy as possible. This is particularly important for newly
transplanted trees.”

Other Borers Likely to
Attack

Braman said other borers likely to attack stressed trees and
shrubs this spring include
flatheaded, longhorned, dogwood and lilac borers and pine bark
beetles.

“Sticky traps, pheromone traps or cone traps are
available,” she said,
“through integrated-pest-management supply companies. The
traps can help monitor the
flight periods of many of these pests. That will help you time
applications of barrier
treatments to the bark of stressed plants.”

Severely damaged pines, such as those injured in the ice
storms of early February, may
simply have to be removed. “It’s best to remove
unsalvageable trees that only act as
beetle magnets,” she said.