Dutch Elm Disease - Overview

Overview

The causative agents of DED are ascomycete microfungi. Three species are now recognized:

• Ophiostoma ulmi, which afflicted Europe from 1910, reaching North America on imported timber in 1928.
• Ophiostoma himal-ulmi, a species endemic to the western Himalaya.
• Ophiostoma novo-ulmi, an extremely virulent species which was first described in Europe and North America in the 1940s and has devastated elms in both areas since the late 1960s.

The origin of O. novo-ulmi remains unknown, but the species may have arisen as a hybrid between O. ulmi and O. himal-ulmi. The new species was widely believed to have originated in China, but a comprehensive survey there in 1986 found no trace of it, although elm bark beetles were very common.

DED is spread in North America by three species of bark beetles (Family: Curculionidae, Subfamily: Scolytinae):

• The native elm bark beetle, Hylurgopinus rufipes.
• The European elm bark beetle, Scolytus multistriatus.
• The banded elm bark beetle, Scolytus schevyrewi.

In Europe, while S. multistriatus again acts as vector for infection, it is much less effective than the large elm bark beetle, S. scolytus. H. rufipes can be a vector for the disease, but is inefficient compared to the other vectors. S. schevyrewi was found in 2003 in Colorado and Utah.