GardenHelp.org

Over the last year I’ve noticed a significant number of Douglas Fir trees (Pseudotsuga menziesii) declining rapidly in my neighborhood. They are showing signs of apical dieback, which rapidly progresses from the tip of the tree downward. All of the trees that I am noticing are

1. On private property so I can’t easily access the roots, soil and trunk too look for more clues
2. Are in on a straight north – south line, between the same two neighborhood streets, running along about 4 blocks

Douglas Fir Showing Apical Dieback

Since I cannot gather complete information, I really cannot diagnose or ask any others to give a complete diagnosis of what is happening. However, I did poll a few very credibly arborists based on the information I know about the trees. Some of the thoughts that came back include:

• No complete diagnosis can be made with just photos and observation (of course!)
• 2001-2005 included the longest and driest drought in Western Washington recorded history. Trees can take years to use up their stored reserved. So, trees with a low survival margin are most suceptible to drought problems. And, trees stressed from drought and then exposed to prolonged rains are more suceptible to root infections.
  • These trees are living, I believe, in rapid draining sandy urban soils. And, at least one of them is surrounded closely by asphalt and houses.
• Root problems often show up first in the crown (tippy-top/apical growth) of a tree
  • Root rots often show up first in the crown of the tree
  • Construction can cause root problems from compaction and other damage.
    • At least two of these trees are near recent townhouse construction
• In areas east of here porcupines bite and strip bark from trees causing these sorts of declines.

So what can be done?

• One professional has found that correct applications of mulcing , mycorrhizae and other benefical materials has brought back over 400 trees exhibiting similar problems.
  • Please keep in mind that these 400+ trees were fully analyzed and diagnosed before treatment began. (Always fully diagnose before treatment, please!)

If you have a Douglas Fir (or other tree) that is showing signs of decline, I suggest having them evaluated by a certified arborist as soon as possible. When trees begin showing signs of decline, they may be significantly compromised in their interior wood and/or in their root systems. Strong winds, ice, heavy rains, drought, snow, insect or other pest infestations, and a host of other factors can cause these trees to decline beyond saving. And, sometimes, it means they are a hazard.

If you would like help determining how to manage a tree issue of your own, please contact me for additional assistance.

In the meantime, I will continue to monitor the trees in my neighborhood. If an opportunity arises to speak with the property owners, I may be able to gather more information to help save the trees. It is very sad to watch these large beauties, which are infrequent in this neighborhood, die.

Read more about this tree here – a new post added February 2009.