Knowledgebase
Chinese Elm Leaf Curl #757737
Asked June 22, 2021, 2:40 PM EDT
District of Columbia County District of Columbia
Expert Response
This looks like damage caused by an insect - particularly the Woolly Elm Aphid, whose feeding causes the leaf distortion, paling of color, and leaves behind white fluffy/fuzzy wax residue. Other aphids in the same genus (Eriosoma) also infest Elms and cause similar symptoms. While Ohio State's article on woolly aphids mentions that this species prefers American Elm and that Asian Elms are not affected, that may not be the case with all aphid species or in our area.
https://bygl.osu.edu/node/1559
Treatment is not needed since natural predators/parasites are likely already working on controlling the population, especially if live aphid colonies aren't currently seen. Additionally, getting the good spray coverage needed to provide satisfactory control via a pesticide is next to impossible with the leaf curls, where the aphids shelter. Such sprays would also harm the beneficial insects. While deformed leaves will not heal, aphid damage should not impact the overall health of the tree. If too unsightly, you can trim off whatever affected leaves you can reach. (We're assuming this is an outdoor, in-ground tree as opposed to a potted bonsai, since Chinese Elm is a popular tree for that use.)
The degree to which the affected tissues are near-white is a bit odd; most Elm Aphid feeding causes a pale yet more yellow to yellow-green leaf discoloration. Was any herbicide used near the elm earlier this season?
Miri