Dutch elm disease
|Dutch Elm Disease|
Branch death, or flagging, at multiple locations in the
|Distribution||Europe, North America and New Zealand|
Dutch elm disease (DED) is caused by a member of the
DED is spread in North America by three species of bark beetles (Family:
In Europe, while S. multistriatus still acts as a
Other reported DED vectors include Scolytus sulcifrons, S. pygmaeus, S. laevis, Pteleobius vittatus and Р. kraatzi. Other elm bark beetle species are also likely vectors.
'Field resistance' is an umbrella term covering the various factors by which some elms avoid infection in the first place, rather than survive it. A clear example would be the European White Elm Ulmus laevis which, while having little or no genetic resistance to DED, synthesizes a triterpene, Alnulin, rendering the bark distasteful to the vector beetles, obliging them to look further afield for more suitable elms. Another would be the inability of the beetles to see elms which did not break the silhouette. 'Weeping' elms are often spared infection owing to the beetles' aversion to hanging upside-down while feeding.
In an attempt to block the fungus from spreading farther, the tree reacts by plugging its own
The first sign of infection is usually an upper branch of the tree with leaves starting to wither and yellow in summer, months before the normal autumnal leaf shedding. This progressively spreads to the rest of the tree, with further dieback of branches. Eventually, the roots die, starved of nutrients from the leaves. Often, not all the roots die: the roots of some species, notably the English elm,