Find, control borers in stone-fruit, ornamental trees soon
The peachtree borer is a serious pest for far more than peach trees. It can attack most trees and shrubs that produce a stone fruit--including plums, cherries, nectarines and apricots--and it merits attention now.
Borers also can infest some of the ornamental, non-fruiting varieties of those plants, said Ward Upham, horticulturist with Kansas State University Research and Extension.
"In fact, peachtree borers often are the real reason behind many Midwest gardeners' belief that purple-leaf plums and sand cherries never live very long," Upham said. "An infestation isn't likely to just catch your eye in passing until it's pretty far along."
Some homeowners' first clue is when a tree cracks off at its base during a windstorm, he added.
"That's why checking closely for borers should be an annual, late-spring chore," the horticulturist said. "Timing is everything to have any hope of controlling these pests."
Kansans usually can achieve best results by spraying the last week in June and again the last week of July, Upham said. That's when the state's annual crop of peachtree borers typically hatches and starts looking for a home, hidden behind a host tree's woody bark.
This month-long hatch corresponds to the year's earlier flight of newly emerged, egg-laying adults--waspy-looking moths. Peachtree borers are the moths' larvae.
"Because these parent moths fly and don't all emerge at the same time, trying to control them is a practical impossibility," Upham said. "Once their newly hatched larvae bore into a tree, the tree's bark becomes effective protection. These insects even stay under bark while they pupate into adults.
"That means you've got to control peachtree borers as they travel between their egg and the place they decide to burrow into a tree. Your window for protecting your tree is actually narrower than the window of opportunity for controlling bagworms."
Peachtree borers tunnel between inner bark and sapwood as they grow, feeding on the bark. This interferes with the tree's flow of moisture and nutrients.
If unchecked, their unseen feeding can girdle and kill a young tree, Upham said. It can injure an older tree so severely that it loses vitality. That loss, in turn, will make the tree more vulnerable to later weather stresses and other insect or disease attacks.
"You can't check for peachtree borers by simply looking for little entry holes, though. They prefer the easy routes, tunneling through cankers, wounds or cracks caused by other factors," he said.
That preference is one reason the first line of defense against borers is to maintain a healthy, vigorous tree, Upham said. This can include watering when needed, ensuring mowers don't injure bark, doing a good job of pruning, and controlling any damaging diseases.
It's also why locating potential "easy routes" is a good way to start scouting for borer activity.
"Pay particular attention to the bottom 12 inches of the trunk," Upham said. "The kind of peachtree borer most commonly found in landscape plants tends to work close to or under the ground. Once they've been at work for a while, you'll also usually find a gummy mass, mixed with sawdust and located on the outer bark, where each borer began its attack.
"In particularly heavy infestations, you may even find pupal cases left behind by the adults that emerged this spring."
Most chemical controls for peach borers are now unavailable for homeowner use.
"Fortunately, though, we do still have permethrin, which is found in numerous products," he said.
Those that list peachtree borers on their labels include such insecticides as Hi-Yield Garden, Pet and Livestock Insect Control; Bonide Borer-Miner Killer; and Gordon's Bug-No-More Yard & Garden Insect Spray.
"Make sure you thoroughly cover the bottom part of the trunk to the point that some spray pools at the base of the tree," Upham advised.
With the decline in control options, some homeowners have been resurrecting older control methods, he said. One of the more popular ones is to use a wire to try to spear larvae inside their tunnels.
"As often as not, though, people end up hurting the tree more than helping it," Upham said. "The better approach is to monitor all susceptible trees and, when necessary, spray the infected ones twice during your area's usual peachtree borer hatch."