by Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension, Benton, Linn and Polk Counties
You’ve probably noticed that incense-cedar (Calocedrus decurrens) is looking pretty ratty in the mid-Willamette Valley this year.
Driving around, I am seeing many trees showing a mosaic of healthy and dead foliage. The dead foliage is reddish to muddy brown and may be individual fronds or small branches. It often seems to be in the lower parts of the tree. Symptoms seem to vary dramatically between trees, even adjacent ones.
So what is going on? Quite likely any of several things.
Incense-cedar rust is a common and familiar foliar disease. It is most recognizable in the spring, when it produces orange gobs of jelly-like goo on the infected fronds. It commonly kills small sprays of leaves and causes a loss of tree vigor in severe cases.
Then there is the less-well-known incense-cedar branch canker which has been showing up in our area recently. It too can cause branch die-back by killing small branches, generally in lower sections of the tree. It seems to hit mature landscape plants. Look for canker lesions and swellings on branches. The canker is sunken, generally a distinct line between live and dead tissue can be seen if you cut back the bark.
Finally, we had a couple periods of record cold weather last winter, with recurring sub-zero temperatures in some areas. I am not seeing injury patterns typical of freeze damage (zones of dead needles, often on the south side of the tree), but suspect that winter temperatures could be a contributing factor.
As I nose around, I’ve found cankers on some trees, and no clear causal symptoms on others. So I cannot blame this die back on any one thing.
Whatever is going on for these individual trees, it is worth noting that incense-cedar is kind of an exotic tree. Sure, it is a native Oregon tree, but it was not a common tree in the Valley historically. We lie at the extreme northern edge of incense-cedar’s native range, a situation where it will likely experience stressful conditions. So it should not be surprising to see it looking ratty from time to time.