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Douglas Fir Tussock Moth |
By Whitney Cranshaw, Colorado State University Cooperative Extension specialist, entomology
The moth lays the eggs, but in the Rocky Mountain region, it's the larvae -- the caterpillar -- that damages spruce, Douglas-fir and true fir. The caterpillars feed on new spruce needles usually starting at the top of the plant and moving down, thinning and discoloring the tree. Heavy infestations can kill tree tops and permanently deform their growth.
The insect overwinters in eggs laid on or around the base of infested trees. This insect is most effectively controlled shortly after eggs hatch in late May or early June. Carbaryl, permethrin or acephate sprays are effective. Successful treatment is dependent on thorough coverage, but densely foliated spruce trees can be difficult to penetrate.
For more information, see CSU Fact Sheet 5.542.
Photo: Judy Sedbrook
