Published on 03/08/00

Insect Pests Boring Georgia Trees, Shrubs

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

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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.

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Photo: Beverly Sparks

Asian ambrosia beetle larvae.

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.

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