Ophiostoma (Ceratocystis) ulmi, Ophiostoma nova-ulmi
Hosts
American elm, Siberian elm
Distribution and disease cycle
Two similar fungal pathogens are responsible for this vascular wilt disease affecting members of the elm family. Since first discovered in North America in 1930, Dutch elm disease has extensively, eradicating many urban, rural and native populations of elm. While Siberian elm is moderately tolerant to the disease, it can still become infected, particularly when weakened by environmental stressors or other pests.
Dutch elm disease is mainly spread by the elm bark beetle, but may also be spread during pruning operations. Beetles breed in recently dead or weakened living trees, with emerging beetles transferring spores from infected to healthy trees as they fly to other feeding or breeding sites. These spores infect healthy plant tissue, spreading internally through water conducting tissue, blocking water movement to branches and eventually the entire tree, resulting in tree death as the disease progresses.
Symptoms and signs
Photo credit: Agroforestry Development Centre
The first symptom of Dutch elm disease is the sudden yellowing of foliage as the disease blocks the water conducting tissue of a branch, eventually causing the branch to wilt and leaves to turn brown. Symptoms spread to adjacent branches as the disease progresses, eventually killing large sections of the tree until inevitably the entire tree is consumed and killed. Disease progression usually takes a few years, but highly susceptible or weakened trees can be killed in a single season. The wood of infected branches will also have brown streaking throughout.
Control
Because other wilt diseases can have similar symptoms, a laboratory test is required for positive diagnosis. If Dutch elm disease is suspected, contact your provincial Dutch elm disease association for more information. If practical, promote healthy trees by providing adequate water during periods of drought. In shelterbelts, pruning and removal of dead and dying elm trees may be required to reduce elm bark beetle habitat. Do not store, transport or use elm plants, wood or chips; burn or bury wood promptly after removal. Remember that pruning elms, including removal of dead/dying branches, is prohibited during times of peak beetle activity (pruning ban: April 1 to Septempber 30 in Alberta and Saskatchewan and April 1 to July 31 in Manitoba), but complete removal of trees with confirmed infections is possible year round. Protectant fungicide injections may be warranted in high value trees, but is generally impractical/ineffective for shelterbelt trees.