Dutch Elm Disease
Dutch Elm Disease (DED) is a vascular wilt disease caused by a fungus. The American elm isextremely susceptible and disease has killed hundreds of thousands of elm trees across the United States. The two insect vectors for transmitting DED are the native elm bark beetle, and the European elm bark beetle. When the adult beetles emerge, they carry the fungus with them when they travel to healthy trees to feed on twigs and upper branches. From the feeding sites, the fungal spores travel to the tree’s water-conducting cells orxylem. Chemicals produced by the tree during its attempt to fight the disease contribute to the plugging of the xylem, causing the tree to wilt. DED can alsobe transmitted from tree to tree through root grafts.
DED is most easily detected during the early summer months when leaves on an upper branch curl and turn gray-green or yellow, and then finally brown. Brown streaks in the wood beneath the bark of affected branches is further evidence,but only true laboratory isolation and identification can confirm positivelythat the tree has DED.
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