This past summer a 70ft, 27"dbh tree, I believe it is Ulmus thomasii,
lost most of its foliage. The leaves dried up over 80% of the crown
and dropped in August. Preliminary investigations have not found sign
of DED. It was suggested that lack of water may have been a factor.
The area is irrigated, no major disturbances within 50ft. Other plants
seem unaffected, save a Scotch pine with mites and bark beetle. This
Elm, according to Dirr, is found on dry slopes and uplands. I wonder
whether others have any ideas?

Reply to post by Kenneth Cote, on December 04, 2000 at 14:36:10:

A wild stab.

Reply to post by jps, on December 04, 2000 at 14:36:10:

Word from Extension Service is that Elm Yellows is not yet in Pacific NW.

Reply to post by Kenneth Cote, on December 04, 2000 at 14:36:10:

Too much water?!

Reply to post by Kenneth Cote, on December 04, 2000 at 17:55:51:

I recently read that the massive oak blight in California is being caused by a Phytophora fungus which mutated from a Phytophora which attacks NW evergreens (cedar, I think). Could this be another mutation? I'm not too familiar with it (interested in finding out more), but I know that leaf drop/defoliation is a primary indicator of the fungi's presence in the oaks.

Reply to post by Kenneth Cote, on December 04, 2000 at 14:36:10:

Consider mites. I had a case (in Delaware) years ago with yellowing and leaf drop, finally identified as an eriophyid mite, on American elms. The foliage dropped yellow, not dried.

Yellows is a possibility, despite claims it isn't there yet. Light brown streaking under the bark near the base, slight wintergreen odor (place bark chips in plastic bag for a few hours).