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The Western Spruce Budworm

Renata saw that one of our spruce trees by the pond has a budworm infection.  It’s common.  I can’t think of a year that one logger or another didn’t stop by the store to visit Dad, and share the arcane knowledge “Mac, you’ve got spruce budworms in your trees.  Need to log ‘em.”  Dad’s reply was always something on the order of “Poor little bugs got to have something to eat.”  And he’d go on letting the trees grow and the bugs dine.

My lazy way of research is to type in the topic, along with the word “extension” and see what someone else has already done on the topic.  In this case, I hit Idaho’s Extension Service, and that’s close enough (having driven across Montana many times, I know how much is grassland.) Randy Brooks is Idaho’s Extension Forester – so I’ll pretty much stick to his publication “ID18 Western Spruce Budworm.”

Here’s the moth form – which I’ve seen through the windows when I’ve left the porch light on.

 And here’s the caterpillar, which has been chewing on the buds.

Now the Western Spruce Budworm has some wide-ranging tastes – Brooks describes it: “Western spruce budworm (WSB) is native insect and is the most widely distributed and destructive forest defoliator in western North America. Susceptible tree species include Douglas-fir, true firs and spruces. Larvae will also feed on pines and other conifers when insect populations reach outbreak levels. Buds, current year foliage, and developing cones are fed on voraciously. Larvae initially feed on new needles throughout late spring and early summer causing a red-halo appearance on outer portions of infested branches.”

In other words, we have a lot of host species, and, in Dad’s words “Poor little bugs got to have something to eat.”  The reality is that

Chemical control over large areas may not be economically feasible, but can be used to protect high value trees from defoliation and associated Western spruce budworm larvae. damage. The materials listed for chemical control in Idaho are carbaryl, cyfluthrin, and spinosad (several trade names). For proper application timing, always read and follow the recommendations on the label. Another management control option is Bacillus thuringiensis (BT), a microbial insecticide which is registered for use against WSB. BT is a naturally occurring, relatively host specific pathogen that affects only the larvae of moths and butterflies. It can be used in sensitive areas along streams, lakes, and rivers. Chemical or BT applications can be conducted from the ground or aerially for short term protection. Users should consult State or Federal Forest Health Specialists regarding formulations, dosage, and treatment timing.”

I suspect that the real challenge of combating spruce budworms around Trego is that it is hard to beat a winged pest that finds so much habitat acceptable.  I could spray BT, year after year, but I think that the Spruce Budworms will eventually outlast me.  Still, Brooks’ article is informative and a good read.

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