Dutch elm disease
July 30, 2015
Ceratocystis ulmi (fungus)
American, English and winged elms.
This disease may begin with yellowing and dieback on a single branch. As the infection spreads, wilting and yellowing of foliage, as well as dieback spreads throughout the crown. Dead leaves remain on the tree. Symptoms are more noticeable when the weather turns hot.
How it’s spread
Drought-stressed trees are more susceptible. The fungus travels within the sapwood of the tree, causing brown streaks; it can be spread from infected trees to healthy ones through root grafts, and by bark beetles carrying spores.
Verticillium wilt also affects elm trees, producing brown streaks in the sapwood. Confirm your field diagnosis by sending a sample to MSU Diagnostic Services for positive identification of the fungus. Left untreated, the disease is usually fatal.
Sever root grafts between diseased and healthy elms. Systemic fungicide injections in conjunction with sanitation pruning (The removal of large limbs at the first sign of the disease.) may be warranted for valuable specimens if symptoms have not progressed too far, but should only be attempted by a qualified arborist. Cut dead trees immediately and remove bark from any elm logs kept for firewood to prevent its use as a breeding site by elm bark beetles.
Elms vary widely in their susceptibility. ‘Regal’, ‘Urban’ ‘Sapporo Autumn Gold’ and ‘Pioneer’ are among the hybrids developed that show resistance. Most of the Asian species of elm are resistant.
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