You’ve probably heard of the invasive emerald ash borer beetles. Now a new insect species is killing Southwest Michigan’s trees. Last Monday, the Gun Lake Tribe announced that they found beech scale insects in Hopkins Township.
Michigan State University researchers estimate that—if left unchecked—the state could lose half of its large beech trees to Beech Bark Disease in the next ten years.
Gun Lake Tribe environmental technicians found beech scale insects on a fallen tree—ironically while looking for invasive emerald ash borer beetles.
Beech scale insects gather in tiny clusters, each scale is no longer than a millimeter. They're often mistaken for white aphids.
“That is the cottony, waxy coating that they exude to overwinter,” says Allegan Conservation District forester Shawn Kelly, pointing to a spot on the fallen beech.
Kelly says the insects themselves don’t cause the disease, but the small holes they make allow a deadly fungus to grow.
“The nectria fungus kind of finds those holes, gets in there and disrupts the nutrient transport up and down the tree, causing the tree to decline,” he says.
Deb McCullough teaches Forestry and Entomology at Michigan State University. She’s researched the spread of Beech Bark Disease. McCullough says beech scale insects typically target trees with rough bark because they’re easier to latch on to.
“Trees that are large and old and kind of gnarly and provide very good habitat for everything from…hawks and eagles like to perch on those trees. All kinds of animals eat the beech nuts that are produced in the fall by big, old beech trees," she says. "And it’s those big, old beech trees that are most vulnerable to beech bark disease.”
McCullough says a beech tree has to be about 40 years old to start producing beech nuts.
Last year, the Michigan Department of Natural Resources found that Beech Bark Disease generally spreads about a mile each year in the Lower Peninsula. In the Upper Peninsula, it’s 2.5 miles a year.
From about July to October, the insects move naturally in the wind or catch rides on animals, but McCullough says they can’t move very far without help from humans. That’s likely how the first two cases of Beech Bark began in Michigan - in Ludington and Newberry.
“And the fact that both of those infestations appear to have originated in camp grounds very widely distant from one another, suggests that somebody may have brought in infested firewood—maybe multiple times there was infested firewood—that had live beech scale on it or the eggs of the beech scale. And that’s how things get started,”says McCullough.
Though the fungus is often fatal, McCullough says Beech Bark Disease isn’t always taken seriously. After all, the disease has been in North America for about 125 years, but it’s relatively new to Michigan.
“It’s not necessarily I would say a ‘relevant species’ in a lot of the Northeastern forests now. In the lake states region, we like our beech. We certainly value the beech—especially as you go north where you lose the oak trees and oaks produce acorns, which is a very important hard mass for a lot of wildlife," says McCullough.
"But as you get further north, the oaks disappear and beech has always been the hard mass producer in the U.P. and northern lower Michigan.”
McCullough says a forest service lab in Ohio is working with MSU and the Michigan DNR to breed beech trees that are resistant to Beech Bark Disease.
“We think about one percent of the American Beech Trees have a natural resistance to the scale insect," she says. "It probably has to do with the chemistry of the inner bark. And the problem for decades was that nobody could vegetatively propagate beech—for whatever reason it’s really difficult to do. And so they’ve made great headway in that and someday there might be some resistant beech trees.”
McCullough says right now—other than scraping the scale insects off the tree before the fungus set in—there’s not much you can do to save an infested beech.
She says insecticides haven’t been proven effective. She doesn’t recommend cutting the trees down either—they’re still a useful resource for animals even after they’ve caught the disease.
As for the Gun Lake Tribe, environmental director Liz Binoniemi-Smith says the best they can do is stop it from spreading.
“Because we did catch it early we can bring local landowners’ awareness up so that they can check out their woodlots to see if there’s already infestation," she says. "I don’t know if we can stop it because it’s wind-born and it’s spread by animals. Those are really factors that are out of our control.”
The Allegan Conservation District is offering free on-site exams for Beech Bark Disease.
