Douglas-Fir Tussock Moth affecting pine trees in Denver

How much damage can a little moth do?

Homeowners around Denver are getting to know the Douglas-Fir Tussock moth, and it’s not a good introduction. Spruces, true firs, and Douglas-firs are dying around Denver as this little moth is making its rounds. Who is the Douglas-fir Tussock moth and how can we stop its destruction?


Douglas-Fir Tussock moth caterpillar

The caterpillars of the Douglas-fir Tussock moth (Orgyia pseudotsugata) are known for feeding on the needles of spruces, true firs, and Douglas-firs. (Colorado State University Extension) Their feeding typically begins at the tops of these trees with the blue spruce being its favorite target along the Front Range. More mature caterpillars can cause significant damage to a tree over the course of a growing season, weakening it to the point of no return.

Natural enemies of the Douglas-Fir Tussock Moth

The good thing is there are several natural enemies of this moth. (Douglas County) Several types of wasps and tachinid fly are known predators who love the taste of Tussock moth. Of course, spiders are a natural predator as well, particularly wolf spiders. Lastly, birds of all kinds find Tussock moth to be a fine meal among the fir trees. All of these natural enemies pose a great role in limiting Tussock moth populations.

How to manage and prevent damage from Douglas-Fir Tussock Moth

There is no known cure for existing damage due to Tussock moths. However, there are some good preventative measures you can take to protect your trees from future infestation:tussock-moths_cranshaw-300x205

  • Young larvae are more easily contained than more mature caterpillars. Mid- to late May are the best times to spray right after the eggs hatch with new Tussock moth larvae.
  • Inspect your trees for egg masses in early spring. This will give you an idea of which trees are at risk. Make note of any vulnerable trees within the eggs’ vicinity.
  • Plant pyrethroids, such as permethrin (Astro), cyfluthrin (Tempo), bifenthrin (Talstar, Onyx), and lambda-cyhalothrin (Scimitar) to deter Tussock moth caterpillars. You can also consider planting carbaryl (Sevin, Sevimol), teburenozide (Confirm, Mimic), and spinosad (Conserve) that are also known to control Tussock moth caterpillars.

If your property has spruces, true firs, or Douglas-firs, they may be the next victim of the Tussock moth. Call Fielding Tree & Shrub Care to schedule an on-site inspection so our team can help you care for and protect your trees. We’re Douglas County’s favorite arborist and we’re here to serve you!