Invasive Species Management

Aug 01

[ARCHIVED] Douglas Fir Tussock Moth

The original item was published from August 1, 2019 8:45 AM to August 4, 2021 5:09 PM

Doug Fir Tussock Moth - caterpillar

Douglas Fir Tussock Moth

Douglas fir tussock moth (DFTM) is a native insect whose populations are increasing in the southern portion of Jefferson County. In 2016 we saw over 24,000 acres defoliated near the Buffalo Creek area. According to the Colorado State Forest Service many of those trees will recover. Landowners in the affected area should monitor their properties and not move items infested with DFTM.

At this time of year DFTM is overwintering in the egg stage.
Landowners in the forested areas in southern Jeffco should be looking for egg masses now to determine if there is a possibility for large numbers of DFTM on their properties. Egg masses can be found on branches and the trunks of trees. The eggs are in a mass of very small pearl like eggs surrounded by grayish brown hairs. The eggs will hatch into very small caterpillars around late May, at the same time the trees will begin to bud. Landowners may decide to treat their trees if they find large numbers of egg-masses. The time to treat is in early spring when trees are growing new needles and the caterpillars first emerge Treatment is not effective after they get larger than about ¼ inch long.
?Treatment is not always necessary if the landowner can tolerate some impact to their trees. DFTM populations tend to subside within a few years. Trees will sometimes rebound but weakened trees may be attacked by bark beetles such as the Douglas-fir bark beetle or Ipps beetle. The Colorado State Forest Service has recently published a factsheet