No need to panic over infested trees

Two different defoliating insects are

to blame for some tree infestations across the Flathead Valley —

western spruce budworm and Douglas-fir tussock moth.

Time to panic? Not yet says the

Department of Natural Resources and Conservation.

“We have been getting frantic calls

from landowners concerned about the number of brown trees on their

property, some even entertaining ideas about massive aerial

spraying,” said Rick Moore, service forester for the DNRC. “We want

to get the word out that this infestation is currently not a

catastrophe.

“We’ve had four summers with cooler

temperatures and normal rainfall, so trees are not as stressed as

in previous years. We believe many of the larger trees are in a

good position to survive these outbreaks, though landowners may

lose some of their understory. We also want people to be smart

about how they react to this infestation and do the right things at

the right time.”

The western spruce budworm is the most

common and most destructive defoliator. Douglas-fir is their

preferred target, though other stressed species can be susceptible,

including grand fir, subalpine fir, spruce, and larch.

This is the third year of budworm

attacks across most of the valley, and their cycle is

unpredictable. That means these pests could do damage for a few

more years before they die out, or they could disappear after a

good hard freeze next spring. The last significant budworm outbreak

in western Montana occurred in the 1980s.

Currently the budworm is in its moth

phase; the moths are coppery brown, about an inch long, and are

probably noticeable around your yard or woods. After they mate, the

female moths will lay eggs on the underside of needles. When the

eggs hatch in late summer and early fall, the larvae will migrate

to tree bark crevices to spend the winter.

The budworm larvae will emerge as

caterpillars in late May or early June next year and restart their

cycle of damage, munching on old needles and buds until new foliage

emerges.

It is during this phase that homeowners

can apply insecticides effectively, the Whitefish Area Fire Safe

Council says. Look for products whose active ingredient is Btk,

Bacillus thuringienses kurstaki, a biological control that is

formulated specifically to address caterpillars. The best time to

apply insecticide is when the buds are just beginning to open.

The tussock moths are more aggressive

but usually die out on their own within two to three years. While

tussock moths prefer Douglas-fir, they also can attack grand fir,

white fir, spruce and other species. This is the second year of

tussock moth infestation in the area, with some neighborhoods

seeing more activity than others.

Currently the tussock moth is

concluding its crown-deforestation phase and becoming more visible

as colorful caterpillars drop from trees on long silk threads. The

tussock moth caterpillars are easily identified by the furry tufts

protruding from their heads and tails and buff-colored, hairy

bodies.

The tussock moth will cocoon shortly on

sides of trees and buildings and emerge as moths throughout the

fall into November. Moths are charcoal brown in color and slightly

larger than the budworm moth. Only the male tussock moth can fly.

Females lay their eggs on the cocoon, and the eggs will hatch in

late May to early June next year. Then their cycle of destruction

begins again.

Treatment used at the right time for

budworm can also help to mitigate tussock moth infestation. The

nuclear polyhedrosis virus is nature’s response to controlling a

tussock moth outbreak. This virus commonly builds up in the

population and ultimately knocks it back.

“Landowners who want to take action now

can consider watering their landscape trees through hot weather,”

said Moore. “Ongoing tree management practices that improve overall

forest health, such as thinning trees and removing undergrowth,

could give trees more vigor to withstand future attacks. Thinned

stands also have a better chance of rebounding when defoliation

subsides.

“Species diversity is also a good

stewardship practice for any forested area,” added Moore.

The Whitefish Area Fire Safe Council

has developed an FAQ concerning this outbreak that provides more

answers to landowner questions. They hope this article and the FAQ

will help landowners make informed decisions on how best to

maintain healthy native trees/woodland around their property. See

www.wafsc.com for details.

— Molly Miller is with the Whitefish

Area

Fire Safe Council.