Question
I live in Southern Minnesota, we have a wind break made up of many Colorado Spruce trees, and the trees are being striped of their needles by something, the moths that fly from the trees are a light tan color- can you tell me what this is and what to use to get rid of them?

Answer
Sounds like spruce budworm.

The western spruce budworm, Choristoneura occidentalis Freeman, is the most widely distributed and destructive forest defoliator in western North America. Several outbreaks have occurred in Colorado, the largest exceeding two million acres. In Colorado, they most commonly infest Douglas-fir and white fir. Occasionally, they also attack Engelmann spruce, blue spruce and subalpine fir.

Western spruce budworm adults  normally are small, mottled, rusty-brown moths, but color can vary from tan to almost black. In Colorado, they are present from late June to early August. After mating, females lay masses of overlapping green eggs on the undersides of needles . The masses consist of 25 to 40 eggs that hatch in about 10 days. The young larvae do not feed but move to crevices under bark scales or lichens where they spin silken shelters called hibernaculae. There they remain dormant throughout the winter

In late April or May, the larvae migrate to the foliage, where they mine old needles or feed on host tree flowers. In a week or two, they enter developing buds, the habit that gives them their name. As the new needles lengthen, the rapidly growing larvae continue to feed. It is during this stage that most of the damage occurs. They web the new foliage together loosely and feed inside, where they are somewhat protected from predators and other enemies.

In the late larval stages , budworms have brownish heads and brownish-olive bodies. Each body segment has two conspicuous pairs of white spots. About 40 days after feeding begins in the spring, usually about the end of June, the larvae pupate inside feeding webs or on foliage. Adults emerge a week or so later and the cycle is complete. There is one generation per year.

Budworms are important because they can eat all the new growth produced by host trees. The new needles are most important in producing food for the tree, so the immediate effect of defoliation is a reduction in growth.

To the homeowner, defoliation mostly means a loss of aesthetic value. As defoliation progresses, both in extent and duration, more significant impacts are likely. The foliage, especially the branch tips, turns brown and dies. Twigs, branches or entire tops of trees may be killed. During long-running outbreaks, three to five years or more, may trees will die. Nonfatal defoliation may also lead to infestation by the Douglas-fir beetle or other bark beetles. In turn, these can kill the tree.


Cultural practices such as  watering and fertilizing, which promote tree vigor, may help trees better withstand repeated attacks. I would fertilize with 10-10-10 fertilizer scattered around the trees and watered in good. Apply just before a rain storm and you will not need to water.


The good thing is they having one life cycle per year they will not be a problem again until next year. The caterpillar stage is the stage that is treated, Chemical control often is used to protect high-value trees from defoliation and associated damage. The materials listed below are registered for western spruce budworm control and have been used with success in Colorado. They can be applied both from the ground and aerially. In either case, time spraying to occur during the two to three weeks immediately following bud break or flush of new growth. In most years, this occurs about mid-June.

insecticides for control of western spruce budworm.
insecticide  Trade name  
Bt (Bacillus thuringiensis) Dipel, Thuricide, Biobit,

carbaryl Sevin