Hello Lynda,

Douglas-fir tussock moth populations can cycle quite a bit from year to year; sometimes infestations in one year are taken care of on their own by natural controls from predators, parasitoids, and disease.

However, if an outbreak persists, several insecticide options are available to kill the caterpillars.  Treatments targeted at the youngest larvae shortly after egg-hatch (typically late May) are most effective.

A list of possible chemical options and wealth of life history information can be found in this CSU Fact Sheet: https://extension.colostate.edu/topic-areas/insects/5-542-douglas-fir-tussock-moths/

I hope this is helpful.

Cordially,

John