Ministry of Agriculture

Dutch Elm Disease

Dutch elm disease (DED) is caused by two species of fungi (Ophiostoma ulmi and Ophiostoma novo-ulmi). It is transmitted from infected trees to healthy trees by two species of elm bark beetles.

To date, no trees in British Columbia have been found infected with Dutch Elm Disease. Introduction of this disease would pose a significant threat to both the nursery industry and to landscape plantings of elm in the province. As one of the few areas in the world still free of Dutch elm disease, B.C. exports over 10,000 elm saplings annually.

Hosts

Elms (Ulmus spp.) are hosts of DED. American elms are the most susceptible. Siberian, Chinese and other elms are generally resistant but can harbour the disease. Zelkova carpinifolia, an ornamental tree in the elm family is also a host.

Distribution 

DED is widely distributed around the world, including Western Asia, Europe, Canada (all provinces except B.C. and Alberta), United States, and New Zealand.

Symptoms

Symptoms of the disease first appear in June or early July. Leaves wilt, yellow and turn brown in the summer, often on one side of the tree. This is followed by dieback of branches and eventual death of the tree. Brown staining can be seen in the sapwood of affected branches by peeling back the bark.

Flagging branches of an infected elm tree. Photo courtesy of Dr. Gary Platford, Winnipeg, Manitoba. Branch dieback on infected elm. Photo courtesy of Manitoba Agriculture, Food & Rural Initiatives.
Dieback and flagging caused by Dutch elm disease. Photo courtesy of Dr. Gary Platford, Winnipeg, Manitoba. Vascular discolouration under bark of infected elm branch. Photo courtesy of Saskatchewan Environment.

 

Life Cycle

Dutch elm disease is transmitted from infected trees to healthy trees by the European elm bark beetle (Scolytus multistriatus), an introduced species which is present throughout Southern B.C.  It can also be spread by the native elm bark beetle (Hylurogopinus rufipes) which is common in Eastern and Central Canada, but is not known to occur in B.C.

The beetles breed in weakened trees in galleries constructed under the bark. Galleries excavated by adult European elm bark beetles are parallel with the wood grain, a feature that can be used to distinguish this species from the native elm bark beetle.

In infected trees, the beetle galleries become colonized by the Dutch elm disease fungus. In the spring, a new generation of beetles emerge which spread fungal spores to healthy elm trees as they feed on branches. Beetle feeding introduces the fungus to the vascular tissue where the fungus colonizes and clogs xylem vessels causing a vascular wilt. The disease can also spread by natural root grafting to adjacent trees.

Long distance spread usually occurs through movement of infested elm firewood or logs. Movement of infected elm nursery stock could also introduce the disease to new areas.

Left trunk: native elm bark beetle galleries;
right trunk: smaller European elm bark beetle galleries.
Photo courtesy Natural Resources Canada, Canadian Forest Service
Smaller European Elm Bark Beetle. Photo courtesy
Thérèse Arcand, Natural Resources Canada, Canadian Forest Service

 

Prevention

Never transport elm wood or wood products with bark to new locations.  Many landscape and forest pests can be spread in firewood. Leave your fire wood at home and pick up local wood when camping or travelling. Don’t take extra fire wood home with you.

A voluntary elm bark beetle management program is being followed by nurseries to prevent beetles from feeding and potentially transmitting DED to nursery plantings.

If planting elm trees, obtain nursery stock only from a local, reliable source.

Early detection is the most important step to prevent the spread of this disease. If you spot symptoms of oak wilt, contact the provincial Plant Health Laboratory for instructions on submitting a sample.

Resources

Updated April, 2010