Dutch elm disease is caused by a fungal invasion of an elm tree’s water conducting vessels. Dutch elm disease is exclusive to elm trees and does not pose any risk to other tree species. Once disease symptoms are observed, tree death can occur in as little as a few weeks. When a tree detects the fungus, it responds by plugging its vessels to keep the fungus contained, but the fungus remains ahead of the tree and essentially the tree causes its own death by cutting off the water supply.
Signs of Dutch Elm Disease
Dutch elm disease symptoms appear 4-6 weeks after infection. The first noticeable symptom is wilting or “flagging” of one or more branches in the upper canopy of the tree. Leaves then turn dull green to yellow and brown, resulting in premature leaf fall. As the infection spreads, the wood beneath the bark becomes discolored as a result of fungal staining.
Residents should learn about this threat to our elm trees and be on the lookout for infested trees. If you suspect Dutch elm disease, call the MDA "Arrest the Pest Hotline" at 651-201-6684 Metro Area, or 888-545-6684 Greater Minnesota or Email Arrest the Pest.
How Does Dutch Elm Spread
DED is spread via beetle transmission and roots grafted with nearby infected trees. The most common method of spread is through beetle transmission. There are at least two kinds of elm bark beetles known to transmit the Dutch elm disease fungus; the European elm bark beetle and the native elm bark beetle. Female beetles lay eggs beneath the bark of dead and dying elm trees and/or firewood with tight bark. Newly hatched beetles emerging from infected elm trees carry the fungus on their body parts. The beetles fly to nearby elm trees to feed causing these trees to become infected with DED. Elm bark beetles feed exclusively on elm trees. Dutch elm disease also can spread into nearby healthy elms through roots that have grown together between two or more trees.