Douglas Fir Tussock Moth (DFTM) is a native insect. Its larval stage (caterpillar) feeds on fir and spruce.
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Overall health of your forest is the best defense. Mixed stands with multiple types and ages of trees seem to be better able to survive outbreaks.
Douglas Fir Tussock Moth (DFTM) outbreaks usually last about 2 to 3 years.
If you decide to treat your trees, starting in May after the trees have budded, you may need to treat every 7 days or so, depending on the insecticide you choose. Douglas Fir Tussock Moth (DFTM) may emerge from their eggs over an few weeks so treatments may need to be spread out. Most of the insecticides registered for use on DFTM are short lived and break down quickly. Please refer to the product's label for specific directions.
At this time government agencies in our area are not planning to treat. DFTM is experiencing large populations in areas that are also near the critical habitat for the federally threatened Pawnee Montane Skipper. The insecticides used for DFTM would also affect the skipper.
Normally Douglas-Fir Tussock Moth (DFTM) is kept in check by pathogens and predators. When those organisms’ populations decline a larger number of DFTM are able to survive.
A normal healthy forest is made up of different types of trees and trees of different ages. Our forests are largely dense, single species, of similar age which makes them more susceptible to invasion by forest pests.