There has been an extensive amount of interest in this topic over the past 3 days. Connie Mehmel with the US Forest Service has provided some additional information below along with extensive details of the Doug Fir Beetle and a proven pheromone method to repel them. Keep in mind though that “repelling” is not the same as “controlling”. It’s simply redirecting existing beetles to a different location…like your neighbor’s trees..
By Connie Mehmel, Forest Entomologist, Okanogan-Wenatchee National Forest Forestry Sciences Laboratory
I recently saw a Lake Wenatchee Info Facebook post with a picture of Douglas-firs on the North Shore that were killed by Douglas-fir beetles. I know it is distressing for residents and visitors to see so many pockets of large dead trees. Douglas-fir beetles have been active along the North Shore for at least the last 10 years. 2007 was a particularly bad year. So what’s going on?
Douglas-fir beetles are native insects that survive by boring beneath the bark of Douglas-fir trees, where they eat the phloem. They prefer large Douglas-firs. They do best when trees are damaged or stressed. Blowdown, flooding, root disease, or drought can all bring on pulses of Douglas-fir beetle activity. The North Shore has plenty of large Douglas-firs. The drought of 2003-2005 weakened these trees, defoliation by western spruce budworm in 2006 weakened them more, and by 2007 they were too stressed to produce defensive chemicals. At least 3,000 trees on the North Shore were killed that year.
2014 and 2015 were both drought years. Patches of dead trees have been showing up on the hillsides again. Trees that are obviously dead (red needles) no longer have beetles in them. Douglas-fir beetles attack in spring and early summer. Trees begin to fade (yellowish-green) in late summer or fall. The new generation of beetles leaves the tree the following spring, about the time the tree turns red. Removing currently infested trees is always a good idea, but it may be hard to identify them in time.
The best prevention is to keep trees as healthy as you can. Promptly remove any Douglas-firs that are damaged. Thin Douglas-fir stands to reduce competition. If there is root disease, it may be advisable to remove the Douglas-firs and convert to a less susceptible species.
There is an anti-aggregation pheromone (MCH) available commercially that will prevent Douglas-fir beetle attacks. I have attached a handbook describing its use. MCH is a very good product, but remember: it does not make trees healthier. Be sure you identify and address the underlying problem.
I’ve attached a leaflet on Douglas-fir beetle which provides excellent photos and information on the insect’s life cycle and controls.
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