How can I tell if my tree has OW or DED?

An oak tree with OW shows signs in June-September during leaf-on conditions. The first symptom is yellow or brown curling leaves moving from the branch tips down toward the main stem, also called “flagging.” The leaves may also start curling with a dark water-stained olive-green color. Next, the leaves drop, like fall leaf drop but occurring during the summer. The disease can kill a red oak rapidly, sometimes within two weeks. The process is usually slower in white oak species. 

Symptoms of DED in elm trees often first appear in late spring and early summer but can occur any time during the growing season. Leaves on one or more branches in the outer crown of the tree will turn yellow before curling and turning brown. Look for fallen leaves strewn on the ground during spring or summer.

If you would like more information on these diseases, visit the University of Minnesota webpage on oak wilt or Dutch elm disease. If you see any of these symptoms on your oak or elm trees and would like an inspection, contact Forestry staff by email at

Show All Answers

1. How can I tell if my tree has OW or DED?
2. What can I do to protect my oaks from oak wilt?
3. What can I do to protect my elms from DED?