Red pine shoot moths leaving their mark across much of Minnesota

If you live near red pine trees — and in much of Minnesota, chances are you do — you may have noticed some dead, brown patches in the upper branches this summer.

They're proof of a moth outbreak the likes of which the state hasn’t seen in more than 20 years.

Red pine shoot moths are usually pretty rare. Rachael Nicoll is a forest health specialist for the Minnesota Department of Natural Resources — and before this summer, she’d never seen a mature one in the wild.

Now she says, three-quarters of all the red pines in her area, north of Brainerd, are infested. The infestation in red pines extends south to the Twin Cities, and north past Bemidji. The DNR reported that on some trees, 80 percent of new shoots are affected.

The moths — in their caterpillar stage — eat and nest in the tender outer twigs of the pine trees. Most of the time they’re kept in check by parasites. But sometimes — and biologists aren’t sure why — their population explodes.

"Luckily (they're) not as destructive as locusts, but their populations are known to fluctuate widely. Generally two to three years of damaging populations are typically followed by seven to 10 years of very low numbers," Nicoll said.

The good news is the moths don’t actually kill trees, just slow down the growth for a few years.

"It’s not a serious outbreak, it’s just a very widespread, and a very interesting and kind of arresting outbreak," Nicoll said. "I mean, once you notice it and realize how widespread it is, (it's) very fascinating."