Douglas Fir Tussock Moth (DFTM)

Hillside of dead trees killed by Douglas fir tussock moth.
Douglas fir tussock moth caterpillar.
Dead trees along river.

What It Is

The DFTM is a native insect that experiences outbreaks every 7 to 10 years. Usually the outbreaks last about three years. Trees will sometimes survive a single defoliation but may not survive repeated attacks. 

DFTM has one generation per year.  It overwinters as eggs.  The eggs begin to hatch in late May at the time new foliage emerges.  Early instars begin feeding on the young tips of the trees, usually near the top of the trees.  As the larvae grow they begin to feed on older needles.  Larvae can be wind dispersed as they hang from silk.  The larvae pupate starting in late-July.  Female moths are wingless and can be found on the tree near where they emerge from the pupal case. Males are attracted to the females through pheromones.  Adults die at the end of the season.  

Treatment of high value trees may be beneficial when populations of DFTM are increasing.  The timing for treatment needs to coincide with the early larval. You should monitor your trees beginning when the buds emerge. CSFS Treatment Guide (PDF)

 

Jan

Feb

Mar

Apr

May

Jun

July

Aug

Sept

Oct

Nov

Dec

Larva





Late-May through July






Pupae







Late-July through August





Adult







Late-July through 

early- November



Egg 

August through late-May



August through late-May

 













Treatment





Mid-May through
 mid-June







Predators

Normally DFTM is kept in check by native predators and pathogens. During outbreak situations landowners may chose to treat high value trees when the DFTM caterpillars first emerge, usually in early May.

2021

July 2021- Neighborhoods near Golden have reported a limited DFTM outbreak.  Owners should monitor their trees for DFTM larvae in spring 2022 at bud-break to access if treatment is warranted.  

2015 Outbreak

In 2015, Jefferson County experienced an outbreak of DFTM in the southern portion of the county.

The U.S. Department of Agriculture Forest Service (USFS) and Colorado State Forest Service (CSFS) monitored the outbreak. Because the federally threatened Pawnee Montane Skipper is known in the area of Jefferson County that was experiencing DFTM activity, treatment choices were limited.