By Amy Grotta and Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension

Group mortality of Douglas-fir in May 2015.  Douglas-fir beetle was found in all these trees.  Photo Kara Shaw
Group mortality of Douglas-fir in May 2015. Douglas-fir beetle was found in all these trees. Photo Kara Shaw

We have certainly experienced some significant drought conditions lately.  Stressed and dying trees are showing up all around the Willamette Valley, with concern that this could lead to beetle outbreaks and still more trees killed.  Is it time to throw in the towel, cut your losses (so to speak) and just salvage everything that is looking poorly?  Maybe, maybe not.  The decision needs to be considered carefully, weighing individual sites and stand conditions along with your objectives for your property.  Anybody considering a salvage harvest needs to look before they leap. Continue reading

By David Shaw, Forest Health Specialist, OSU Forestry and Natural Resources Extension

Douglas-fir killed by drought
Douglas-fir killed by drought

The summer of 2015 is shaping up as a big year for drought and drought related forest health issues throughout Oregon, but especially in the Willamette Valley, SW Oregon, and in Eastern Oregon.

In late summer, it can be very difficult to discern whether insects, disease, or drought and heat are causing tree dieback and deaths, but we are becoming pretty confident that drought and heat together are influencing much of what we see.  In this report I outline and describe some of the more common problems we are seeing with conifers and hardwoods as of early September.

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By Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties

drought stressYoung Douglas-fir trees with dying branches or tops turning brown, then red have become a common sight all around the Willamette Valley this spring. What is going on?

This “flare out” of branches and tops are classic drought symptoms in Douglas-fir, which we are linking to last year’s weather when we had a particularly long, dry and very hot period late in the summer. Late season drought injuries to the stem and leader do not always show up when they occur, but often express themselves the following spring as trees start to grow. We have these drought damage events from time to time here in the valley, most recently in 2013 and again before that around 2000. Older trees typically have milder symptoms, but the many older, flat-topped Douglas-fir trees you see are a reflection of past droughts and non-fatal damage. Continue reading

drought stressThe phone has been ringing off the hook lately with calls from people describing sick and dying Douglas-fir and other conifer trees. The trees are of a wide range of ages and in many environments and settings, although most calls have been coming from within the valley margin and have to do with young trees.

So far, the answer is generally: “It is drought stress”.  Huh, in May? Well it has been a dry winter and spring, … but that is not the issue.

My best explanation is that we had a pretty hard end of summer last year. Remember that? NO rain until mid-October then, Boom, it was winter. By then, many trees had started running out of water, killing tops or branches, and leaving leaders and branches susceptible to attack by various opportunistic pests.

We started seeing a few classic signs of drought stress (tops dying and branches “flaring out”) at the very end of the season last year, but late enough that many did not have time to show up before the weather turned. Injuries had occurred, so it was just a matter of time before they expressed themselves, which is happening now. The recent hot weather seems to have made it more sudden and dramatic.

This happens from time to time. Here are two good articles a few years back by the ODF Forest Health team explaining Dead tops and Branches (with Good pictures), and about Drought and Mortality.

It is important to keep in mind that the Willamette Valley can be a challenging climate for trees. Many of our soils in the valley are poorly drained, which is hard on most of our conifers, and other soils are fairly shallow and cannot hold much water. Also our summers are hotter and drier than in the mountains. Heat and drought stress can kill trees outright, or more often just put the trees under stress, which can then lead to pest problems (as explained in the two publications above). From what I am seeing and hearing, the major cause of the problem now seems to be drought stress. Insect or diseases which able to take advantage of a stressed tree’s condition may sometimes be involved, but they are generally not the cause of the problems.

Finally, weather can be more stressful when trees are overcrowded, so thinning stands to keep trees vigorous with adequate growing space may be helpful in the long term. Right now, we just have to wait it out, and hope we get some serious rain this year, or we will see this problem intensify.

We all better get out there and wash the car…..

Brad Withrow-Robinson