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New insect pest hits Colorado’s beleaguered forests

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Pine needle scale directly affects the needles of conifers. Photo courtesy Oregon State University.

Outbreak on pine needle scale  reported in Grand County, ground zero for the pine beetle infestation

By Bob Berwyn

SUMMIT COUNTY — Colorado forest health experts say there’s a new pest on the loose in one of the areas hardest hit by mountain pine beetles.

Pine needle scale is affecting patches of trees in Grand County, where residents have reported ailing lodgepole pines in recent months.

The tiny bug latches on to pine needles and sucks them dry. They can affect any age tree and generally don’t cause trees to die, although a heavy infestation can lead to mortality, according to Ryan McNertney, assistant district forester for the Colorado State Forest Service Granby District.

“We always see some amount of pine needle scale in the woods,” McNertney, said. “But this year we are seeing whole areas where infestations are so bad that they are actually affecting the health and vigor of the trees.”

Pine needle scale is a native forest insect that generally keeps a low profile. The scale is usually held in check by nature, with cold weather and predatory insects such as lady beetles keeping populations at relatively low levels.

But at higher population levels, infestations of the insect can easily be identified by the presence of numerous hard, white spots dotting pine needles of infested trees – each spot about the size of pencil tip. The spots represent a waxy, protective coating the insects create once they latch onto a pine needle, where they will remain permanently to feed on sap.

McNertney said many landowners in Grand County are calling in and describing their lodgepole pines as being a dingy green or yellow color. This damage can in extreme cases lead to premature loss of needles and twig die-back.

“We have been seeing the largest number of affected trees in the Fraser Valley.  However we have seen impacted areas throughout Grand County. We have not seen large outbreak areas in Summit County,” McNertney said. “I am not really sure on acreage as  it seems to be in spots throughout the county.”

Some forest ecologists describe pine needle scale as yet another natural change agent that helps prune older branches, adding organic material to forest soils.

With the mountain pine beetle epidemic fresh in everyone’s minds, McNertney understands that landowners are worried that their trees might die from the needle scale, but it generally does not cause tree mortality. Large outbreaks of these insects are rare in Colorado, and seldom last long.

“Generally outbreaks are short lived because of the impacts of local population controls like cold temperatures, lady beetles and parasitic wasps,” said Colorado State Forest Service entomologists Skye Stephens.

Damage to trees can include discoloration of needles and the sight of the insect (aesthetic damage) and when severe or persistent (uncommon) can lead to tree mortality, especially in smaller trees, or branch and limb mortality.

“However, in some of the most heavily infected areas I believe there is a good possibility of some trees dying,” McNertney said. “We have seen trees that are completely covered in scale and I’m not sure the trees will be able to recover from some heavy defoliation.”

There is little that landowners can do to combat these insects, especially after they have formed the protective white scales. McNertney said some landowners may opt to use horticultural oils and insecticidal soaps to kill pine needle scale, but warns that these measures may only dry the tree out and cause further damage.

The CSFS Granby District serves Grand, Summit and Eagle counties. For more information about pine needle scale or other forest insect and disease concerns, contact the district at 970-887-3121 or visit csfs.colostate.edu.

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