By: Paul Schattenberg, Texas A&M AgriLife Communications
DALLAS – Dr. Mike Merchant, Texas A&M AgriLife Extension Service urban entomologist based in Dallas, said “there’s a new bug in town” — and it could cause serious harm to some of the state’s most extensively used landscaping trees.
“Ash trees are used extensively around the state in landscaping for homes, businesses, in parks and along highways and streets,” Merchant said. “And the emerald ash borer, an insect that can potentially cause great harm to ash trees, is typically found in more northern states. However, this insect has recently been found here in Texas.”
Merchant said the Texas A&M Forest Service, along with the U.S. Forest Service, recently discovered four emerald ash borer beetles, Agrilus planipennis, in an insect trap in Harrison County, near the Louisiana border.
“Although no actual infested trees have yet been discovered in Texas, these beetles signal a change in fortune for most or all of our state’s ash trees,” Merchant said.
Merchant said he saw many dead ash trees along highways, in parks and in yards during a visit to Indiana last year.
“The borer has been active there for many years,” he said. “It was hard to find a single healthy ash tree, unless it was likely treated with a protective insecticide.”
Merchant said the borer is native to Asia and has already killed tens of millions of ash trees throughout the U.S.
“The emerald ash borer is known to attack only ash and a related tree known as white fringe tree, Chionanthus virginicus,” he said.
Merchant said ash borers usually attack a tree first in the upper parts of the canopy, so damage is usually far advanced by the time emergence holes or damage are seen on the lower trunk of the tree.
“The first sign of an attack is vertical cracks in the bark, usually accompanied by woodpecker damage,” he said. “Woodpeckers are the most important source of emerald ash borer mortality, but unfortunately they cannot prevent beetle attack.
“When foraging for borer larvae, woodpeckers typically leave bark flaking or “blonding,” which is often visible from the ground, even in the tops of trees. In addition to flaked bark, woodpeckers leave behind irregular peck-holes where they have probed for the beetle larvae under the bark.”
Merchant said as the emerald ash borer attack progresses, bark cracking continues and the upper ash canopy will show signs of thinning.
“As the canopy dies back, suckers or epicormic shoots may appear at the base of the tree or on the trunk,” he said. “Epicormic shoots, or water sprouts, grow from the base of trees after stress or injury to compensate for the loss of productive leaf surface. These shoots appear as vigorous new growth below the damaged parts of the tree.”
He said another sign of emerald ash borer infestation is the presence of S-shaped tunnels and frass, a fine powdery discharge or perforation produced by the activity of the boring insect, under the loosened bark of the tree.
“If you see looping, S-shaped, frass-filled galleries under the bark of your ash tree, you have convincing evidence of emerald ash borer attack,” he said.
He added another sign may be 1/8-inch-long, D-shaped holes in the bark of the tree.
“These are emergence holes, used by the adult form of the insect to leave the tree in search of a mate — and the next ash tree to attack,” Merchant said. “The sizes and shape of the holes are important. Holes longer than 1/8 inch or those that are round rather than flattened on one side were not made by the emerald ash borer.”
Merchant said trees affected by the emerald ash borer typically die two or three years after becoming infested.
“Currently 26 states are under quarantine restrictions for shipping of ash wood,” he said. “In the United States, 16 ash species are susceptible, and Texas is home to seven of them,” he said. “And while the Texas A&M Forest Service says ash trees make up less than five percent of rural Texas forests, they are a large portion of landscaping in urban areas.”
He said the Texas A&M Forest Service is working with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, the Texas Department of Agriculture, AgriLife Extension and the U.S. Forest Service, as well as other state and federal agencies, to implement a state response plan.
“State and federal officials have tried to reassure the Texas timber industry that, at least initially, any impacts to the forest products industry should be low,” Merchant said. “And the Texas A&M Forest Service has established a new website so Texans can follow the progression of these insects and learn what steps can be taken to protect their ash trees.”
For more information, go to https://tfsweb.tamu.edu/eab/.
“If you have an ash in your backyard there is little immediate threat unless you live in Harrison County or an immediately adjacent county,” Merchant noted. “Experience with the borer in other parts of the country suggests that there is no need to treat your ash tree unless your home is within 10-15 miles of a known infestation, and that still has not occurred anywhere in Texas.”