The tussock moth caterpillars feed on needles of spruces, Douglas-fir and true firs. When populations are high they can feed on pines and shrubs that are intermixed with Douglas-fir, however they prefer fir. Sporadically outbreaks of Douglas-fir tussock moth occur in several Front Range communities. Less commonly it occurs as a forest pest in Colorado. Numerous natural enemies attack Douglas-fir tussock moth and these will often control outbreaks after a season or two.
At this time the tussock moth is active in Douglas County in the area from Perry Park to Valley Park west of Highway 105, areas off of Dakan Road, and in the area west of Pine Creek Road. Activity is occurring on both private and US Forest Service lands. Larvae have been observed in the Woodmoor Mountain area, along Madge Gulch Road and Sugar Creek Road, however defoliation in these areas has been minimal to undetectable.
The larvae have been feeding since late May and most feeding activity has stopped. Larvae are migrating from affected trees to areas where they will cocoon and turn into adult moths. Residents in affected areas may see significant amounts of larvae on homes and other structures during this process.
There is nothing that can be done about the damage that has occurred and there is no preventative spray that can be applied to non-infested trees. Spraying is not recommended at this time.
- They are a native insect to our forests and have been a common occurrence in the South Platte Watershed.
- Eggs hatch in late May (usually with bud break) and larvae start feeding on the new growth first. You will usually see needles that have been partially eaten and then turn brown. They start near the top of the tree and then work their way down. Young larvae primarily travel by wind to other trees.
- As the larvae mature they will feed on older needles and will be full grown by mid-July-August.
- In mid-July-August the larvae spin cocoons, pupate, and emerge 10-18 days later as moths. The moths mate and lay eggs that will hatch next May. Depending on the location they can lay eggs into September.
- Young larvae are more effectively controlled than older larvae so the best time to spray is shortly after egg hatch, which is in late-May.
- There are natural predators (ex. wasps) and viruses that usually control the population. Outbreaks usually last 1-2 years and then the population returns to non-damaging levels.
- Trees may survive if defoliation is not heavy, however, the damage can make trees more susceptible to bark beetle attacks (ex. Douglas-fir beetle, Douglas-fir pole beetle) as the trees will be stressed.
- Caterpillar hairs can be irritating to the skin and may cause a localized rash. Limit contact with caterpillars and cover exposed areas when working around infested trees
Residents should check their trees next year (May) and if/when they see the tussock moth larvae emerge they can spray at that time to be most effective in reducing damage to trees. Trees should also be monitored for signs of bark beetle attacks next spring.
For more information please visit http://csfs.colostate.edu/districts/franktown-district/