Invasive insect is threatening Minnesota’s oak trees, DNR says
You could call Alicia Hagerty ‘the oak tree whisperer.’
“They’re really majestic trees,” she says. “They go back centuries of importance to people.”
Hagerty, an arborist for 11 years, and the owner of Arbor Gold Tree Services in Plymouth, is fighting to save oaks from an invasive insect called the twolined chestnut borer.
She says in the last two years, she and her team have found more than 1,500 oaks infected or at risk of infection by the borer.
The beetles crawl through damaged spots in a tree and lay their larvae inside, which feed on the inner layers, essential for growth and production.
“Twoline is a little black beetle that tunnels through the trees,” Hagerty notes. “It kind of lives underneath the bark of the tree and it tunnels through the vascular system, essentially destroying it.”
The Department of Natural Resources says twolined borer damage has been spotted in more than three dozen Minnesota counties, from Lake of the Woods to the north, Houston in the south, Otter Tail to the west, and Chisago to the east.
Still, no one knows the exact scale of this beetle invasion.
“So, the populations are increasing and because of that, we’re seeing more and more trees affected by it,” explains Megan O’Neil, a forest health specialist with the DNR.
Just ask John Racek.
Looking skyward from his Hopkins backyard, you can see the damage.
In one corner, there’s an intact tree canopy. In another, blue skies- and missing trees.
Racek has lost at least seven mature oaks to the two lined borer.
“It’s nature,” he says, with a rueful smile. “They’re dropping leaves and you’re not really sure if it’s an early fall or it’s truly something going after the trees.”
Experts say despite our recent spring rains, previous dry seasons have weakened the trees’ natural defenses.
Storm damage or even pruning at the wrong time can create entry points for the borers.
“It’s an opportunistic pest,” declares Eli Sagor, with the Cloquet Forestry Center at the University of Minnesota Extension. “It kind of waits for a tree to get sick, waits for a tree to get stressed out, say in this case, from multiple years of drought across much of the state. When that tree is weakened, the twolined chestnut borers kind of overwhelm it.”
Experts advise giving oaks at least one inch of water per week can help protect them from the borer.
That’s because healthy, non-stressed trees will not attract borer adults- and regular watering minimizes drought stress.
The DNR also says if you have concerns about your trees, you should contact a licensed arborist.
For her part, Hagerty says she’s been able to treat and protect 18 of Racek’s oak trees from the borers.
She notes if they’re discovered soon enough, a tree can be saved.
One preventative method Hagerty uses is an injectable insecticide, which kills the borers, but doesn’t harm the tree.
“If it’s caught soon enough, before it has catastrophic damage from the bug inside of it, before it’s vascular system is dead, it can be treated,” she explains. “So, the sooner they look at them, the sooner they’ve been treated, the success rate goes up.”
You can find out more about the twolined chestnut borer by CLICKING HERE.