High Country foresters report rising infestation of pine needle scale
It looks like lice on your trees.
Unprecedented infestations of pine needle scale — a native insect that eats the needles of pine, spruce and fir trees — are on the rise on private lands in the High Country, and foresters have linked the increase to heavy pesticides used to combat mountain pine beetle.
The insecticides may have killed off other insects like predatory beetles and parasitic wasps that typically keep pine needle scale in check.
“It’s really the lack of beneficial insects that’s the driving factor, ”said Ryan McNertney, assistant district forester for the Colorado State Forest Service Granby District, which covers Summit, Eagle and Grand counties. Other environmental factors, like drought and warm temperatures, may have also made trees more susceptible.
Occasional needle scale infestations are common in Colorado mountain forests and typically last for one or two years with minimal impacts. However, Ron Cousineau, district forester for the CSFS Granby District, said the current outbreaks have been more widespread and have continued for the past four to five years in some parts of mountain valleys.
“These infestations have become so heavy and persistent in some areas that we are seeing many trees die with no other insect or disease influence,” Cousineau said. “We have never seen pine needle scale become this damaging in this part of the state.”
A WHITE DUSTING IN THE SUMMER
The bugs have been particularly destructive to blue spruce in Vail and lodgepole pines around Fraser in Grand County. Pockets of pine needle scale infestations have been found on private land in valley areas throughout Summit County.
Foresters have found the largest infestations in or near places that were sprayed with carbaryl and other chemical pesticides over the last decade to control mountain pine beetle, McNertney said, and they haven’t found on public lands where spraying was limited.
“We didn’t recommend that because no one knew what the additional effects would be from that much spraying in isolated areas,” he said. “Unfortunately, with the way the pine beetle happened, it was either spray your trees or lose your trees.”
White River National Forest silviculturist Brett Crary said pine needle scale has not been an issue on national forest lands and can be more of an aesthetic concern for private property owners.
He added that the infestations are associated with urban areas where dust is kicked up and mosquito spray is used that kills pine needle scale’s natural predators.
The pine needle scale bugs are orange, red or brown in color and so small they must be seen with a magnifying glass.
They enter a crawling stage for a couple months in the spring and summer, and, when they stop moving for the rest of the year, they produce a white protective coating called scale that makes trees look like they’re spattered with white paint.
The insects feed on needles, and, eventually, they cause needle fall and dieback. Scale infestations also can lead to higher vulnerability to other insects and diseases.
“The infestation has to be pretty darn high and sustained for several years to kill the tree,” McNertney said. For the most part, infected trees will look strange but rebound as beneficial insect populations return.
TO SPRAY OR NOT?
For worried property owners, horticultural oils and insecticides may reduce impacts of scale infestations if applied during the insect’s crawler stage, which McNertney said is typically from late May to early July in the High Country depending on weather.
Don Clark, maintenance department manager at the local landscaping business Neils Lunceford, said he is still seeing the bugs bump around this summer and expects they will finish the crawling stage in mid-August.
Once an effective treatment is applied and kills the insects, the white scale part may remain like the shell of a dead oyster, Clark said, but “the tree just looks so much more perky and more healthy.”
The Colorado State Forest Service is working to determine the best ways to minimize further impacts from the needle scale outbreak, and for now, foresters warn against further chemical spraying of impacted trees.
“If we can minimize tree stress, that’s a key to keeping the scale populations low,” McNertney said. “The more proactive management we can do to keep healthy forests the better off we’re going to be when something like this arises in the future.”
He recommended property owners follow defensible space recommendations and, in general, thin mature trees so their crowns are about 10 feet apart and they aren’t competing for resources.
For more information or a site visit, call the Colorado State Forest Service Granby District at 970-887-3121.
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