Ash tree stress
The leaves on our ash trees are turning brown and mottled and have been dropping since late July. This has been happening for several years now and some neighborhood trees are now dead. Can you identify the problem and recommend a solutions?
Clackamas County Oregon
Thanks for your question about your poor ash trees! There are two diseases that have been identified in ash trees in Oregon. The first is verticillium wilt, a soilborne fungal disease; here's link to an OSU article on the wilt, with pictures of infected ash trees, Another airborne fungal disease is Chalara dieback; here's a link to an article on the dieback. I can't tell from the pictures you sent whether there stem lesions or not, and the wilt is identified by cutting open the stems, and seeing a dark brown/black color in the xylem. (It can also be diagnosed through a soil sample.)
The sad 'news' is that neither pathogen is treatable. Here's a list of plants susceptible to verticillium wilt, as well as resistant ones.
Hope this helps.
Thanks for the fast response. I have attached another picture showing some of the leaves that are remaining and the stem. I also remember that very tiny white larvae were dropping out of at least one of the trees about a month ago.
One of the problems of diseased trees is that they attract insects (since they're easier to penetrate). And, since the larvae that you saw have now eaten their fill--hence the notched leaves--are now adults and have flown off to find mates, it's hard to ID them. You might want to visit this site to see if you see any signs of the ash borer: insect.pnwhandbooks.org/hort/landscape/hosts-and-pests/ash-fraxinus-borer