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In the fall, after a long, dry summer, an evergreen conifer may not have enough resources to sustain all of its green foliage; thus, it will shed its oldest foliage (i.e., the foliage found on the innermost part of a branch). In doing so, the tree is prioritizing its resources. The oldest foliage is the least productive because it has become dirty over time and, being on the interior of the branch, receives the least amount of sunlight. The tree will sacrifice this older foliage in favor of the newer, more productive foliage.
Ladd Livingston, Idaho Dept of Lands, bugwood.org
Although the tree’s appearance may be somewhat alarming, this seasonal foliage loss is a normal part of conifer growth. The foliage loss is particularly noticeable in western redcedar, where it is referred to as “flagging.”
Seasonal foliage loss can also be particularly pronounced in pines. Some years seem to have particularly pronounced seasonal dieback, depending on weather patterns and other stress factors. Thus, even when a tree has excessive interior needle loss, it is not necessarily an indicator of disease, insect attack, or other unhealthy conditions. There are some insects and disease agents that tend to attack a tree’s oldest foliage, but these agents usually leave signs of their activity, such as chewing or speckling across the older foliage.
You’ll find more information about seasonal foliage loss here.
Submitted by: Tim Kohlhauff, September 21, 2015
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