Douglas Fir Tussock Moth (DFTM)

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)

Predators

Normally DFTM is kept in check by native predators and pathogens. During outbreak situations landowners may chose to treat high value trees.  Treatment should be timed to 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. The federally threatened Pawnee Montane Skipper is known in the area of Jefferson County that was experiencing DFTM activity so treatment choices were limited.