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

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3 thoughts on “Stressed and Dying Conifers: Another year for “Valley Crud”

  1. Thank you for this information. This is exactly what I am seeing in my fir trees, but not so far in the pine trees. I have been very concerned about it, but figured (correctly) that I would just have to wait it out. At least I now have a something that I can call it, when I talk about it.

  2. Can one place a bucket that drips under the tree, btw how much water would such a tree need through drip, … my neighbor who is from a Middle Eastern Country says that mid size (including fruit) 5 – 25 feet high trees needs 5 to 10 gallons once per dry week during summer. He says it helps these trees find their own resources way down, … and that also creates pathways for water from rain to the lower
    underground areas, …

  3. We live near McKenzie Bridge, and have planted over 3,500 trees. While this article addresses mostly the valley, our trees – too – have been affected. We now plant “plugs,” not bare root, so we know die-off is not from J-roots, L-roots, or planting depth. These trees are like our babies – die-off is distressing (speaking of stress).

    Most of our planted die-off is Douglas-fir and Western Red Cedar; but self-seeded Grand fir seems just as susceptible to ‘drought stress.’ We have had some mortality from Ponderosa Pine (which we re-plant to replace other dead varieties, and does seem much hardier); we suspect it might be the voles (although I haven’t been able to spot any ‘girdling.’

    That said, I appreciated the article. Thanks!

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