Spruce Budworm Infestation Will Only Get Worse
by Phil Miller
Jul 24, 2008 | 574 views | 0 0 comments | 7 7 recommendations | email to a friend | print

The infestation of the spruce budworm that was reported on the July16 KOTO news is considerably more widespread than Lawson Hill. It extends all along the north-facing slope from at least the Telluride Park where I ground checked it, to, likely, the head of the valley. I could see farther east with binoculars what appears to be branch tip damage toward Bridal Veil Falls. I traced the infestation to the west side of the Silver Pick road and lower side drainages that flow into the San Miguel River from the south. Many of the spruce trees in town are affected. Most or all of the Douglas fir trees on the north side of town up the south facing slope show terminal branch damage. I saw budworm branch tip damage on trees as I walked a short portion of the Wiebe Trail. I walked the Telluride Trail from the San Sophia Station and found affected trees all the way into town.

The infestation spills over the crest of the Coon Skin ridge into Mountain Village. It is not so obvious as on the valley side, but it is there. I drove Benchmark Drive to Hood Park checking trees as I went. A breakout of an insect infestation does not happen suddenly, it only seems to, as when people in the Lawson Hill development suddenly saw lots of little moths fluttering around and noticed that the branch tips of spruce and fir trees were turning brown. The budworm undoubtedly was in the Lawson Hill area last year and probably some years back. But this year, it seems, almost instantly the moths were all over the place. When conditions are favorable over several years, the insects increase year to year exponentially. One year nobody is aware of them. The next, nobody can miss them. The level of the infestation in the Mountain Village hasn’t reached the point where it is noticeable. You have to look carefully for them and know what to look for.

The extent of much of the infestation can be seen from a distance because the tree branch tips look brown as if they were scorched. Four species of our local conifers are susceptible to attack by the budworm, subalpine fir, Douglas fir, blue spruce, and Engelmann spruce. Douglas fir and subalpine fir are preferred by the budworm. Along the river banks and a short distance above, the dominant coniferous species is blue spruce, as is the principal conifer planted in town for landscaping. Blue spruce and Engelmann spruce are the most likely to escape serious damage from the budworm. The dominant tree species downvalley on the north facing slopes of the San Miguel River is Douglas fir. If this infestation becomes so serious that it results in heavy mortality we will see the biggest losses in the Douglas fir stands. There are already many dead firs down valley killed by the Douglas fir bark beetle that has happened within the last five or more years.

The budworms have passed from the larval stage, emerged from the pupal stage and are now adult moths. They do their damage in the early summer larval stage when they feed on the buds of the branches and the tender flushing needles. The female adults lay their eggs on the undersides of the tree needles. The eggs hatch in about ten days, but the hatching larvae do not feed. They seek sheltered places in the tree bark to over winter.

“The western spruce budworm is the most destructive forest defoliator in Western North America.” Western Forest Insects. U.S. Department of Agriculture, Forest Service, Miscellaneous Publication No. 1339. Defoliation damage by the budworm isn’t serious in our area so far. But next year’s attacks may be far more damaging. I saw moths everywhere along the bike trail from Lawson Hill along the top of the Coonskin ridge. Infestations are likely to span several years, each year’s a step up in destructiveness. A tree may recover from a 50-to-75 percent defoliation for about three years before dying, unless, being in a weakened state, it succumbs to bark beetles sooner. The most serious budworm infestation locally broke out on the Uncompahgre Plateau five to ten years ago. It was most damaging to subalpine fir so that the coniferous forest along the Divide Road on the Plateau with its dead and damaged trees which includes Engelmann spruce, presents one of the sickest forests of conifers I have ever seen in my 59 years as a professional forester. The infestation was not as serious in the spruce as in the subalpine fir.

So what can we expect of this infestation? We don’t know.
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