Courtesy of Chris Hedstrom/Oregon Dept. of Agriculture
Invasive, crop-damaging insects such as Spotted Wing Drosophila, Japanese Beetles and Brown Marmorated Stink Bugs cause alarm and get research attention, but the latest problem bug to emerge is a home-grown pest that hasn’t been a factor for decades.
Researchers in Oregon and Washington say they’re hearing reports of damage from Pacific Flatheaded Borers, a beetle that seeks out weakened plants and can kill young fruit and nut trees. Oregon State University staff recently found several damaged trees in its new cider apple nursery beds, which were planted as a research response to the increasing popularity of hard cider drinks.
Nik Wiman, an assistant professor and orchard specialist with OSU, said he knows of a young commercial cherry orchard that was hit hard and said the borers are a threat to “All those brand new hazelnut trees out there.”
The damage to trees is caused by the beetle larvae, which bore into trees and chew “galleries” or “mines” between the bark and wood. They can “girdle” and kill a young tree by chewing their way all the way around it.
Wiman and others said borers are a difficult pest to work with because there are no traps or pheromones developed to attract them. Spraying for them is problematic because they spend much of their life sheltered under bark. They begin to emerge in late spring, but there doesn’t seem to be a regular schedule for that.
To that end, Wiman is collecting infected wood from damaged trees, the idea being to rear larvae under controlled conditions and learn more about when adult beetles fly. “We want to get an emergence curve,” he said. “We want a predictive model.”
Flatheaded borers are not a new pest. Scientific literature on the borer dates to the 1930s or 1940s, but it hasn’t been studied for decades, said Betsy Beers, a professor and entomologist at Washington State University’s Tree Fruit Research and Extension Center in Wenatchee.
“We’ve seen so little of it here in Washington, I think most entomologists have forgotten about it,” Beers said. “The ones I saw a couple of years ago were the first ones I’d seen in my professional career.”
In that case, damage reports surfaced from tree nurseries in British Columbia. Washington State obtained borer larvae and reared them as a research project.
An OSU Extension publication from 1982 said the boring larvae almost always begin their work on the sunny side of a tree, and may bore 1 to 2 inches deep. If they tunnel all the way around, they can kill the tree or infested branches. Growers should look for darkened areas of bark and fine bits of sawdust low on the tree.
Adult borers are up to a half-inch long, with metallic copper-colored spots on their wings, according to the OSU publication.
The adults fly for three to five weeks and make a buzzing sound when flying, according to the publication. “They are active insects, and will quickly conceal themselves or fly away when approached. Being sunlovers, they are inactive and rarely seen on cloudy days,” it said.
James LaBonte, an entomologist with the Oregon Department of Agriculture, said Flatheaded Borers and similar pests take advantage of trees damaged by equipment or weakened by sunburn, drought or even excess water. The act of planting can stress young trees as roots are disrupted, he said.
“Anything that makes a tree feel less than great is going to set them up for attack,” he said. “All of these can predispose these plants to attack.”
Extreme weather swings, whether brought on by climate change or not, may bring on more insect damage to stressed trees, LaBonte said.
He said Christmas tree growers, for example, are seeing more damage from the Douglas Fir Twig Weevil, which doesn’t kill trees but can reduce value by making them look ugly.
“I anticipate we will see more of this,” he said.