Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties.
Conifer trees around the Valley continue to show signs of severe drought and heat stress this year. This should not be news to many readers: young dead trees are now a common sight throughout the Valley. Also, I wrote about this problem in past Tree Topics blogs (See stories from May and September 2015 for background) but have new updates for this season.
I think you can expect to continue seeing similar damage to Douglas-fir this year and that symptoms will continue to unfold as the season progresses. Some of the trees damaged late last year did not show that damage immediately. The damage did not become evident until the trees came out of dormancy and began to grow this spring. Also, the various insect and disease organisms that take advantage of weak and damaged trees are likely to continue with their business this year, causing new signs of drought damage to show up during the season. Happily, those players like Douglas-fir cankers and twig weevils do not typically blow up and kill healthy trees. This suggests things will look much like what we saw and described last year and is likely to continue to unfold this season and maybe longer, whatever weather we get. “It is important to understand that the effects of drought damage do not go away suddenly when the rain starts again” cautions Christine Buhl, ODF Forest Entomologist “drought can impact the tree’s whole plumbing structure, and affect the growth and vigor of the tree for years.”