The predominantly Douglas fir forests of the Wood River Valley could be in for a shock. The "most widely distributed and destructive defoliator of coniferous forests in western North America," the western spruce budworm, is at work in the Smoky Mountain foothills on the west side of the valley.
Fresh waves of rust-colored trees are spreading near Greenhorn Gulch, about midway between Ketchum and Sun Valley, and at Owl Creek, just south of St. Luke's Wood River Medical Center. The U.S. Forest Service has asked an entomologist to examine the outbreaks, and that should happen next week, said Kurt Nelson, district ranger for the Sawtooth National Forest's Ketchum Ranger District.
Nelson said preliminary investigations show that western spruce budworm could be responsible for the outbreak at Owl Creek. The Douglas-fir tussock moth could be at work near Greenhorn. But officials aren't yet certain which of the two insects is at work in each location or the extent to which these natural processes have taken root.
"That's why we're having the entomologist come up," Nelson said.
The budworm and tussock moth have similar lifecycles. They both produce one generation each year. Adult moths from both species appear in late summer. Both are fond of Douglas fir trees, which larvae use for food. One key difference is budworms spin silken tents called "hibernacuila" in which they remain inactive through the winter. The other thing they have in common is that they can both take a serious toll on Douglas fir forests, killing or weakening trees in potentially widespread areas.
Nelson said the spruce budworm outbreak could be significant because there hasn't been one in this area for between 14 and 20 years. What's more, he said there has never been a tussock moth outbreak documented south of Galena Summit in this part of Idaho. Both species range throughout the Northwest, southwestern Candada and throughout parts of the Rocky Mountains.
Other tree-killing organisms at work in the Wood River Valley's Douglas fir forests include the dwarf mistletoe, a parasite, and Douglas fir beetle. The mountain pine beetle is at work in the Sawtooth Valley, where it has killed millions of lodgepole and whitebark pine trees in the last six years.
Check them out
For information on the Western spruce budworm: www.na.fs.fed.us/spfo.pubs/fidls/westbw/fidl-wbw.htm.
For information on the Douglas-fir tussock moth: www.na.fs.fed.us/spfo/pubs/fidls/tussock/fidl-tuss.htm.
