Asian Beetle Pesters U.S. Ornamental Tree Industry

OVERTON, Texas, May 11, 2004 (ENS) - The Asian ambrosia beetle is now appearing in devastating numbers and is wreaking havoc among the Southern U.S. ornamental tree growing industry this year, researchers say.

A research team investigating methods of controlling the pests warns that a good part of the $225 million East Texas nursery industry is at risk from the invasive beetle, which also threatens pecan orchards and species such as redbud, ornamental pears and red oaks.

The tiny beetle is known to attack more than 100 species of trees, but seems to favor and do more damage to juvenile trees such as those found in tree nurseries.

Less than three millimeters long, the miniscule beetles can kill a tree in a few weeks.

"We have some growers who have lost whole species of trees this year," said Dr. Scott Ludwig, a Texas Cooperative Extension integrated pest management specialist.

"I heard very little about the beetle from the growers the first two years I was here," said Ludwig, who has been working in East Texas for three years.

No one knows why the insect made such an impact this year, but Ludwig said it is suspected that mild winters have played a big role.

The adult beetles overwinter in leaf litter, and warmer winters could result in more insects surviving to emerge in the spring.

"But that is just conjecture at this point," Ludwig said. "We do not know for sure."

Ambrosia beetles are so named because they cultivate the ambrosia fungus inside the tree.

The pest does so for the same reason that a number of ant species farm fungi, to produce food. The fungus plugs up the tree's vascular system, the collection of tiny vessels that transports water and nutrients to the plant cells.

"It is really the ambrosia fungus that kills the tree, not the beetle," said Ludwig, who has launched an two-fold emergency program to deal with the threat.

One program, funded by the U.S. Department of Agriculture, is the testing of a new preventative trunk spray at two nurseries. The other is a trapping survey to find out just how deeply the Asian ambrosia beetle is entrenched in East Texas.

Ludwig designed the survey to monitor when the adults emerge from the trees and determine what other species of ambrosia beetle are present.

Once a tree is infested, no chemical controls will save it. A tree may be infested by a single beetle or by hundreds.

For juvenile trees, up to three years old, the infestation most often proves fatal.

Mature trees are more likely to survive the infestation but may serve as staging base for the beetle to attack nearby younger trees.

For this reason, the general control strategy is to cut down and destroy any infested trees immediately.

"The quandary comes when a favorite mature tree is infested," he said. "No one wants to cut down and burn an otherwise healthy tree, but not doing so could endanger new trees in the area."