Tussock Moth Caterpillars Hatching Now

Forest Health - BeetleBusters has been watching Douglas-fir Tussock Moth eggs in northwest PBH. Caterpillars began hatching on May 24th, on schedule. If you have Doug-fir on your lot and have cocoons nearby, now is the time to spray Bt-k (bacteria that harms only caterpillars) to the tops of trees you want to keep.

Caterpillars are about 2 millimeters long when they hatch. They climb to the tops of Doug-firs and eat tender new needles. If they ingest Bt-k, they die. It is important to spray trees now, when the caterpillars are young.

Tussock Moth Cocoon

The Douglas-fir Tussock Moth cocoon is about one inch long, and tiny black caterpillars hatch from the eggs around the end of May. Look for these cocoons on trees and structures and report their location to foresthealth@pinebrookhills.org.

Nearby Tussock Moth Damage

The photos at left were taken from Wild Horse Circle, looking out half a mile to the west. Click on each image to load it in full resolution.

And click here for a printable Tussock Moth advisory.

What to Do About the Douglas-Fir Tussock Moth

The only treatment for an infected tree is to spray it with chemical or biological insecticide when larvae hatch in late May (timing is critical). Bruce Benninghoff, our forest health consultant, recommends spraying Bt (Bacillus thuringiensis), a naturally occurring soil bacteria that is ideal for controlling various leaf eating caterpillars including Tussock Moth larvae. It will not harm people, pets, birds, honeybees, or other beneficial insects. The spray must reach to the top of the tree. The caterpillar hairs and cocoons can induce a severe rash, so do not touch either.

Learn more about Bt here.

How to Find Where Douglas-Fir Trees Grow

Not sure if you have Douglas fir trees on your property? Learn how to find Doug firs here.

Doug Fir Tussock Moth

From: Bruce Benninghoff (bruce@frontrangeforestry.com)

Significant impacts by the Tussock Moth have been reported on Cheyenne Mtn by Colorado Springs, Near Perry Park, the Rampart Range, and northwest of Boulder. This is not to be confused with the western spruce budworm, although both are defoliators of spruce, Douglas fir and white fir.

For more information on the Tussock Moth, see the Colorado State Forest Service Quick Guide and the CSU Extension Sheet.

Also see photos at left:
Tussock Moth In Hand
Tussock Moth Larva
Tussock Moth Cocoon on DF sapling
Tussock Moth Cocoon on stump

The cocoons are typically attached to trees but they may be almost anywhere, trees of other species, rocks, logs, sheds, in firewood piles, loosely stacked lumber, etc.

The larva should be maturing and forming their cocoons in which they pupate about this time of year. I found the cocoon in the picture near Aspen Park this week.

It is too late in their life cycle to treat for them now.
HOWEVER, I encourage you to look for the larvae and cocoons as a way to gauge the population.
If you have a large number this year it gives you the basis for being prepared to spray to control them next year.
Timing is critical as the treatment must be done when the larvae are young.
Timing is weather dependent.
Neighbors and contractors must be all lined up in advance in order to get the spraying done at the right time.

Note: The hairs on the larvae and cocoon are irritating to some people. They may cause a nasty rash.

Please let me know if you find any. If you have questions or want help looking for them, give me a call.

Bruce Benninghoff, Consulting Forester
Benninghoff & Company