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Dutch Elm Disease Prevention

Dutch Elm Disease (DED) is caused by the elm bark beetle, which spreads sac fungi to elm trees– the fungi then clog the vascular system of trees, preventing water to reach the crown.

This eventually causes the tree to wilt and die.

Managing DED

DED must be managed through the disruption of the disease cycle– by sanitizing early in the progression of DED the population of beetles is limited, which in turn limits the spread of fungi.

Also important is the use of chemical insecticides to destroy the insects and prune away any initial infection. Breaking root graphs between neighboring trees also plays a role.

Signs and Symptoms of DED:

Wilting leaves it the first sign of DED– the leaves turn from a vibrant green to a yellow brown. Fungi may be spread through grafted roots, meaning that symptoms may begin in the lower parts of the tree on the side of the root connection.

When spread this way, the damage to the crown is both fast and severe– it begins at the end of each branch, a process known as ‘flagging’, and will then progress downward through the crown of the tree.

Symptoms normally start at some point during the growing season- normally late spring. In cases where the tree was infected in the previous season and the disease has not been treated, the symptoms will be noticeable in early spring as the leaves begin to grow.

The progression of the disease is different from tree to tree– some trees are entirely affected in one season, while others may take several years.

DED also causes dark streaks in the tree branches– this discoloration can be detected by peeling off a strip of bark on a branch that is dying and exposing the outer rings. If the branch has been recently infected, the brown streaks will not yet appear in the sapwood.

If the tree was infected during the previous season, the discoloration may not affect the current sapwood, so it’s important to cut deeply into the wood or investigate a cross section of the branch.