Douglas-fir tussock moth defoliates Douglas-fir, spruce and true fir tree species, including white fir.
Douglas-Fir Tussock Moth
Douglas-fir tussock moth is a defoliator of Douglas-fir. The moth is a native species found throughout mixed conifer forests in the western United States.
- Adult male moths are gray-brown to dark brown with feathery antennae and a wingspan of about 1 to 1¼ inches.
- The wingless female moths have small thread-like antennae and a large abdomen, which may be filled with eggs.
- Mature larvae are about 1-1¼ inches long and have four cream-colored tufts of hair, or tussocks, with an orange-red-colored band on top are located behind the head and at the rear of the larvae, giving these moths their common name. The rest of the body is covered with short tufts of hair radiating from red centers.
Symptoms of Infestation
In Colorado, isolated outbreaks tend to be cyclic in nature and may occur in intervals of seven to 10 years. Tree defoliation is the most conspicuous symptom of Douglas-fir tussock moth infestation. Defoliation typically begins at the top of infested trees and progresses downward. Upon closer inspection, damaged trees should reveal the presence of Douglas-fir tussock moth life stages (larvae, pupae, etc.).
Douglas-fir tussock moth damage can be confused with damage caused by western spruce budworm (Choristoneura freemani Razowski) and, in some cases, both insects may be present. The main difference in damage caused by the two insects is that while Douglas-fir tussock moth can feed on both new shoots and older foliage, western spruce budworm larvae restrict their feeding to expanding buds and current year’s foliage. Also, Douglas-fir tussock moth doesn’t produce silken webbing on trees, a common characteristic of western spruce budworm.
Treatment options vary based on the size of the infestation and the desired treatment area.
- Individual, high-value trees can be effectively treated with biological or chemical products, provided the entire tree is treated – especially the upper crown, where damage is typically concentrated.
- Larger forested areas can be effectively treated with biological or chemical products, applied by either helicopter or fixed-wing aircraft. Aerial application of insecticides over forested areas poses a higher risk of danger to non-target organisms, including aquatic insects, fish and/or organisms that may be rare or endangered, than ground-based applications.
- Timing is critical and most effective in the spring when new needles emerge and the larvae will be feeding on the new growth, increasing the likelihood of contact or ingesting the product.
Learn More About Douglas-fir Tussock Moth
Douglas-fir Tussock Moth (5.4 MB PDF)
Treatment Options for Douglas-fir Tussock Moth (8.9 MB PDF) – New 2016