HELENA, Mont. (AP) — While the mountain pine beetle epidemic has passed its peak, Montana forestry officials said Monday it's not over yet.
The latest survey shows more than 526,000 acres of pine trees in the state were infested with the beetle in 2013, officials told the Board of Land Commissioners.
That amount is still significant as the insects continue to leave stands of dead trees in their wake, said Amy Gannon, pest management specialist with the Department of Natural Resources and Conservation Forestry Division.
"People think the mountain pine beetle is done, but it isn't," she said.
The most active outbreaks remain in the southern part of the Bitterroot National Forest and in the Big Hole area in the Beaverhead-Deerlodge National Forest.
Since 2000, the epidemic has spread across more than 6 million acres, or 23 percent of the state's 25.6 million acres of forest on private, state and federal lands.
The beetles, which are native insects, attack older stands of trees, most commonly lodgepole and ponderosa pine. The beetles bore through the outer bark and into an inner layer of a host tree, where they feed and lay eggs, according to the natural resources agency.
The feeding activity, combined with a blue-colored fungus they introduce, kills the trees.
Mountain pine beetle activity generally is declining as the insects run out of trees to attack in western Montana, Gannon said.
But another pest is attacking and killing a rising number of Douglas fir trees, Gannon said. The Douglas-fir beetle's activity increased in 2013 to nearly 16,000 acres, the report said.
It's not necessarily the overall number of acres that's notable, Gannon said, but the increase in acreage and broad area in which the beetles are found.
Much of that increase is associated with the western spruce budworm, which Gannon said was also among the most damaging insects in 2013.
Budworms harm trees by eating pine needles and buds, making them more susceptible to Douglas-fir beetle infestation, according to the department. Budworms were found on approximately 596,000 acres mostly in Flathead, Lewis and Clark, Lincoln, Missoula, Park, and Powell counties.
Gov. Steve Bullock, who is chairman of the Land Board, asked Gannon during the meeting if cold weather can kill beetles.
Gannon said it can kill them only at about 40 degrees below zero, and only if those temperatures last several days. Generally, temperatures haven't been cold enough at the right times to do more than slow beetle activity in certain locations, she said.
Active management techniques such as thinning trees in dense areas, breaking up continuous landscapes and addressing root disease can minimize the impacts of the pests, Gannon said.