Douglas-Fir Tussock Moth (Orgyia pseudotsugata) and Spruce Budworm (Choristoneura hebenstreitella)
Populations of these two defoliating caterpillars continue to expand this year in the Colorado Springs area. Blue Spruce, Douglas Fir and White Fir are hosts to these insects. Larvae were observed hatching in early June and evidence of feeding on new growth is just starting to show up.
The caterpillars of both moths feed on the new needles, eventually moving on to older needles and stripping the branches. After the initial season of feeding, a tree can usually put out new growth the following year, but with repeated defoliation a tree will die or become prone to bark beetles. It is important to spray for these insects. Chemical controls should be applied shortly after egg hatch in May or early June but can be applied into July if the caterpillar is still on the tree. A biological option, Bacillus thuringiensis, is also available and effective for early instar stages of the caterpillar. It is a bacterium that feeds on caterpillars. Timing is critical and it is not as effective as other control options.