Calocedrus decurrens dieback
Been noticing substantial dieback on Calocedrus decurrens in the Portland Oregon Metro region. First started noticing it in the Spring, and has definately gotten worse. Large stretch of affected trees along Hwy 26 on the North side of the Highway just west of the Sullivan Tunnel. The pattern of dieback seems to be fairly random, affecting medium to large specimens; in what I believe is mostly non-irrigated landscapes. From what I have observed, dieback usually occurs first in the lower half of the tree canopy and from there moves to various spots within the canopy. Any ideas on what is happening to these trees and if anything is being done to mitigate loss.
I and others have been observing the same thing. At this time there is no clear understanding of the causal factor, although there are a number of pathogens that affect incense cedar, including a foliar rust and a branch canker. I've seen evidence of both of these on various trees over the last two seasons. A recent article describes in more detail:
P.S. I'm not sure where the Sullivan Tunnel is...is that the name of the tunnel between downtown Portland and the Zoo?
Thanks for your question.