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OVERTON – Long a threat, the Asian ambrosia beetle is now appearing in devastating numbers. This insect is wreaking havoc among the Southern U.S. ornamental tree growing industry this year, according to a Texas Cooperative Extension integrated pest management specialist.
Dr. Scott Ludwig and other IPM specialists have embarked in a search for an economically sound means of controlling the pests, which puts part of the East Texas $225 million-a-year nursery industry at risk. The pest also poses a risk to pecan orchards and other species, such as redbud, ornamental pears and red oaks.
"We have some growers who have lost whole species of trees this year. 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.
Ludwig 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.
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's really the ambrosia fungus that kills the tree, not the beetle," Ludwig said. No one knows why the insect made such an impact this year, but Ludwig said it's suspected that mild winters have played a big role. The adult beetles over-winter in leaf litter, and warmer winters could result in more surviving to emerge in the spring, he said. "But that's just conjecture at this point. We don't know for sure," Ludwig said.
Ludwig noted a few products are labeled for use as a preventative trunk spray, but most are either marginally effective or require multiple sprayings throughout the growing season, a practice that is both expensive and labor consuming.
More effective controls were once available, but as their labels expired, they were not re-licensed by the U.S. Environmental Protection Agency. This was because either the chemicals were considered hazardous or the chemicals' manufacturers lost interest because of the cost of re-licensing.
The product Ludwig is testing is less hazardous more environmentally friendly and allegedly lasts for as long as two months, he said. Having a dependable control is vital to the industry. 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 an eight-inch long, the beetle can kill a tree in a few weeks. It burrows into the trunks of susceptible tree species, pushing out a mixture of sawdust, tree sap and its own feces as it goes. This mixture, called frass, hardens into a thin stick about the size of toothpick that juts out horizontally from the tree trunk 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, 1 to 3 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. If local ordinances permit, burning the tree is the best way to ensure the beetles are destroyed as well. If open burning isn't permitted, and the tree is small enough, it can be ground up and composted, Ludwig said. "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."
Writer: Robert Burns, 903-834-6191, rd-burns@tamu.edu
Contact: Dr. Scott Ludwig, 903-834-6191, swludwig@ag.tamu.edu