Watch the elm for yellowing of the leaves, followed by wilting and browning. Look for vascular discoloration to help with diagnosis of this disease. Peel back the bark of a symptomatic branch to reveal the brown streaks in the otherwise tan outer sapwood. We generally select branches that are about as thick as a thumb with wilted leaves. Verticillium wilt and Dothiorella wilt can also cause this streaking in elm.
Positive identification requires laboratory culturing of the fungus.
The fresh wood sections should be thumb thickness and can be sent in plastic or foil to the Plant Clinic for testing. Chilling the wood should not be necessary with suspect samples. Expect about seven days of lab time for the fungus to grow to the point where it can be positively identified. For more information on DED, including control procedures, consult Report on Plant Disease No. 647. A similar disease caused by a phytoplasma is discussed in RPD No. 660, Elm Yellows or Phloem Necrosis and Its Control.