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Dutch elm disease

Written by Ramsfield, T.D. Revision 2025

Infected elm tree
Infected elm tree Pierre Desrochers

General information and importance

Dutch elm disease, so called because the disease was first described in the Netherlands, is caused by the fungal pathogens Ophiostoma ulmi and O. novo-ulmi. It affects multiple species of elm (Ulmus) in Europe and North America and is spread by bark beetles that attack elm trees. The disease was first discovered in Canada in Quebec in 1944, and it is hypothesized that O. ulmi arrived in infected elm wood crate material that was used to package machinery from Europe at the outbreak of World War II. A second pathogen, the more virulent O. novo-ulmi, was introduced into Canada more recently and has become the dominant pathogen that causes Dutch elm disease. The pathogen, and the resultant disease, has since spread within Canada and is causing extensive damage to elms in most of the country. The economic costs associated with the management of affected trees, and the loss of amenity value that occurs when boulevard trees are removed, are high. Affected cities within provinces where the disease is present conduct management activities to slow the spread of the disease. Within provinces that are currently free of Dutch elm disease, there is a concerted effort to prevent the establishment of the pathogen in these areas.

Distribution and hosts

Dutch elm disease is established in most of Canada, with the exceptions being the provinces of Alberta and British Columbia. The native American elm (Ulmus americana), rock elm (U. thomasii), and slippery elm (U. rubra) are all highly susceptible and the disease can be found throughout the natural range of these hosts in Canada and in the United States. The introduced Siberian elm (U. pumila) and Japanese elm (U. parviflora) are moderately resistant to the disease. Although still under investigation, eastern Asia is the most likely native range of the pathogens.

Tree parts affected

Vascular tissues of twigs, branches, and trunk.

Symptoms and signs

The first symptoms of the disease are yellowing and browning of leaves on infected elm branches, followed by wilting and defoliation. As the pathogen spreads within the tree, wilting and the number of dead branches increases. The pathogen can grow down the main trunk from the point of infection to the roots, ultimately killing the tree. Initial wilting may be visible in the first year of infection and trees can die within 1 to 4 years.

A cross-section of an infected branch will reveal dark rings in the outer sapwood and discoloured xylem tissue. Signs of the sexual state of O. novo-ulmi are black long-necked perithecia (base globose, 75‒140 micrometres wide; neck: 19‒36 micrometres at base, 9‒14 micrometres at tip; and 230‒640 micrometres long), that produce ascospores (hyaline, single-celled, orange segment-shaped, 4.5–6.0 micrometres × 1.0–1.5 micrometres). These fungal structures are present within beetle galleries.  

Disease cycle

The pathogen is transported from tree to tree via spores that are adhered to the exterior of elm bark beetles. There are three bark beetle species that are attracted to dead and dying elms and act as vectors: native elm bark beetle (Hylurgopinus rufipes), European elm bark beetle (Scolytus multistriatus), and banded elm bark beetle (S. schevyrewi). The latter two species are not native to North America and have been accidently introduced from Europe. The pathogen relies on these beetles for long distance dispersal. These beetles burrow into elms where they mate, excavate galleries, and lay eggs. During the beetle infestation process, the pathogen becomes established in the tree as the spores attached to the beetle are shed and moved by sap flowing within the tree’s vascular tissues. Following establishment in the tree, the pathogen spreads in the vascular tissue, eventually to the main stem and roots. Once the pathogen is present in the roots, it is possible for infection to be transmitted to other elm trees via root grafts. Beetles mature into adults under the bark of the diseased tree where spores of the pathogen become adhered to the adult beetle and the pathogen is then spread by the adult beetles that emerge and fly to nearby trees.

Damage

As the vascular tissue of a branch becomes plugged by tyloses, water transport is inhibited, and foliage on the affected branch yellows, wilts, and is shed. The pathogen also produces a toxin, cerato-ulmin, that contributes to wilting. As a result, dead branches appear in the otherwise healthy crown of the tree. As the infection progresses down the tree, other branches become infected, and when the pathogen enters the main trunk, it can travel down to infect the root system. At this point, the tree succumbs to infection and dies. In highly susceptible hosts, death can occur within a year of infection, although it takes longer in more resistant hosts. Regarding ecological impacts, Dutch elm disease has resulted in a large decrease in the prevalence of elms throughout their native range in eastern and central Canada. The most devasting effects can be seen on American elm populations, of which 95% were killed by the disease. However, some young and medium-aged elm trees can still be found in the wild, but these relatively few elms often do not attain the sizes they did before the introduction of the disease because older trees will often be preferentially attacked by one or more of the elm bark beetles. Dutch elm disease has had a significant impact on urban elm trees too. In Montreal, nearly 90% of the city’s elm trees succumbed to the disease from 1970 through 1980, and Toronto had lost 80% of its elm population by 1976. Elms play an important role as shade trees in many urban areas and many western Canadian cities are actively managing to either prevent the introduction of this disease to their urban elm populations or reduce tree losses where the disease has become established.

Prevention and management

Pest management strategies for a particular pest vary depending on several factors. These include:

Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.

To prevent the movement of beetles to new host trees, cities have imposed pruning bans during the time that beetles are active. The dates of the pruning bans can be obtained from city websites. Active management activities should be maintained within cities where the disease is present to keep the population of the pathogen as low as possible and to minimize tree losses. If dead branches are noticed by urban arborists, the affected branches must be removed and infected material burnt to destroy the fungus and beetles living in the branch tissue. From a public safety perspective, it is also important that these dead branches, or dead trees, are removed to prevent public injury should a dead branch fall. Favouring more resistant species of elm, such as Siberian elm, for amenity plantings is good practice.

To prevent the establishment of the pathogen in disease-free cities, adherence to rules related to the movement of firewood must be observed and enforced to prevent unintentional long-distance movement of beetles that carry the pathogen. Within Alberta, the Society to Prevent Dutch Elm Disease (STOPDED) organization provides outreach materials to educate the general population and prevent the establishment of the pathogen in the area.

In cities free of Dutch elm disease, arborists should be trained to identify symptomatic trees. Material from symptomatic trees should be collected and the presence of the pathogen confirmed in the laboratory. If the pathogen is confirmed, diseased trees should be removed as quickly as possible to prevent the establishment of a population of the pathogen within the city. A beetle-trapping program, centred around the area where the pathogen was first detected, should also be initiated so that the distribution of the pathogen can be understood. If trees killed by Dutch elm disease are not removed, they will become a source of pathogen inoculum that will be later distributed by beetle offspring that were attracted to the dead trees, thus lowering the probability of successful eradication. As trees are replaced on the landscape, tree species that are immune to the pathogen should be favoured. There are also efforts underway to breed disease-resistant elms.     

If the pathogen is not successfully eradicated, a long-term management strategy will be required. Management activities include annual surveys to remove infected trees and the removal of dead hazard trees. The protection of high-value trees may be accomplished through stem injection of approved fungicide by a licenced applicator. Pesticides registered for use against the pathogens that cause Dutch elm disease under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered pesticides and product information for use against these pathogens. The application of any registered product should be based on population size and applied only when necessary and against the approved life stage. It is also recommended to consult a local tree care professional. Pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and follow to all directions and precautions noted on the manufacturer’s label. In some jurisdictions and situations, only a licensed professional can apply pesticides. Consulting relevant local authorities to determine local regulations that are in place is recommended.

The economic costs associated with Dutch elm disease are high. In areas that are disease-free, outreach to the public should be conducted because avoiding the introduction of the disease is the first step in protecting urban elms. If a diseased elm is discovered in a new area, every effort should be made to eradicate the disease. Eradication activities are expensive; however, the costs of management activities, coupled with the loss of expensive elm trees, are greater.

Photos

Leaf wilt

Leaf wilt

André Carpentier

Infected sap-conducting vessels, under the bark

Infected sap-conducting vessels, under the bark

Claude Moffet

Infected elm tree

Infected elm tree

Pierre Desrochers

Leaf wilt

Leaf wilt

André Carpentier

Wilt and dieback caused by <em>Ophiostoma ulmi</em>, the causal agent of Dutch elm disease, on a white elm.

Wilt and dieback caused by Ophiostoma ulmi, the causal agent of Dutch elm disease, on a white elm.

Brown vascular staining caused by <em>Ophiostoma ulmi</em> in a white elm with Dutch elm disease.

Brown vascular staining caused by Ophiostoma ulmi in a white elm with Dutch elm disease.

Selected references

Bernier, L. 2022. Dutch elm disease. Pages 291–309 in Forest microbiology. Volume 2: Forest tree health. https://doi.org/10.1016/B978-0-323-85042-1.00010-0

Brasier, C.M. 1991. Ophiostoma novo-ulmi sp. nov., causative agent of current Dutch elm disease pandemics. Mycopathologia 115: 151–161. https://doi.org/10.1007/BF00462219

Campana, R.J.; Stipes, R.J. 1981. Dutch elm disease in North America with particular reference to Canada: success or failure of conventional control methods. Canadian Journal of Plant Pathology 3(4): 252–259. https://doi.org/10.1080/07060668109501361

Dunnell, K.L.; Bergdahl, A.D. 2016. Dutch elm disease. Pages 126–128 in Diseases of trees in the Great Plains. A.D. Bergdahl and A. Hill, technical coordinators. United States Department of Agriculture, Forest Service, Rocky Mountain Research Station. Fort Collins, Colorado. General Technical Report, RMRS-GTR-335. 229 p.
https://www.fs.usda.gov/nac/assets/documents/research/publications/rmrs_gtr335.pdf [Accessed October 2025]

Government of Alberta. 2024. Society to Prevent Dutch Elm Disease (STOPDED). https://www.alberta.ca/society-to-prevent-dutch-elm-disease [Accessed March 2024]

Hiratsuka, Y.; Langor, D.W.; Crane, P.E. 1995. A field guide to forest insects and diseases of the Prairie Provinces. Natural Resources Canada, Canadian Forest Service, Northwest Region, Northern Forestry Centre. Edmonton, Alberta. Special Report 3. 297 p.

Hubbes, M. 1999. The American elm and Dutch elm disease. The Forestry Chronicle 75(2): 265–273. https://doi.org/10.5558/tfc75265-2

Karnosky, D.F. 1979. Dutch elm disease: a review of the history, environmental implications, control, and research needs. Environmental Conservation 6(4): 311–22. https://doi.org/10.1017/S037689290000357X

Magasi, L.P.; Urquhart, D.A.; Harrison, K.J.; Murray, D.M. 1993. Three decades of Dutch elm disease in Fredericton, N.B. Natural Resources Canada, Canadian Forest Service, Atlantic Forestry Centre. Fredericton, New Brunswick. Information Report M-X-185E. 39 p.

Martín, J.A.; Sobrino-Plata, J.; Rodríguez-Calcerrada, J.; Collada, C.; Gil, L. 2019. Breeding and scientific advances in the fight against Dutch elm disease: Will they allow the use of elms in forest restoration? New Forests 50: 183–215. https://doi.org/10.1007/s11056-018-9640-x

Pomerleau, R. 1961. History of the Dutch elm disease in the province of Quebec, Canada. The Forestry Chronicle 37(4): 356–367. https://doi.org/10.5558/tfc37356-4

Cite this fact sheet

Ramsfield, T.D. 2025. Dutch elm disease. In J.P. Brandt, B.I. Daigle, J.-L. St-Germain, A.C. Skinner, B.C. Callan, and V.G. Nealis, editors. Trees, insects, mites, and diseases of Canada’s forests. Natural Resources Canada, Canadian Forest Service, Headquarters. Ottawa, Ontario.Ramsfield, T.D.