Dutch elm disease: what the agencies record
What Forest Research, the Canadian Food Inspection Agency and Ontario say about Dutch elm disease: the two fungi, the elm bark beetles that carry them, the symptoms by season, the Canadian regulated areas and elm pruning bans, and what each lists for management.
Checked against the sources at the bottom of this page on October 8, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the official source says. It is not legal advice: ask the office named here. It lists what agencies record about Dutch elm disease and does not diagnose any tree. The list of other diseases is on the tree diseases page, and oak wilt, another beetle-carried wilt disease, is on the oak wilt page.
At a glance
| Item | What the sources say |
|---|---|
| Pathogen | Two related fungi, Ophiostoma novo-ulmi and Ophiostoma ulmi. Forest Research says almost all cases are caused by O. novo-ulmi. |
| Hosts | Elms. Forest Research names English elm, smooth-leaved or field elm and wych elm, and also Zelkova trees. The Canadian Food Inspection Agency names American, rock and slippery elm as highly susceptible. |
| United Kingdom | Present in all parts of the UK. Forest Research says there is no requirement to report suspected cases to the forestry or plant health authorities. |
| Canada | Regulated areas cover Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Quebec and Saskatchewan. Alberta and Newfoundland and Labrador keep a DED-free status. British Columbia is called partially infested. |
| Report to | For Canada, see the Canada report-a-pest guide. For the United Kingdom, see the United Kingdom report-a-pest guide. |
How the sources say it spreads
Forest Research says the fungus passes from tree to tree on elm bark beetles, especially beetles of the Scolytus group, and names the large elm bark beetle as a major carrier in the UK and continental Europe. The Canadian Food Inspection Agency names three beetles: the smaller European elm bark beetle, the banded elm bark beetle and the native elm bark beetle. It says the beetles are drawn to freshly pruned, sick, weak and dying elms, and that the fungus also passes through grafted roots between neighbouring elms and with moved elm material, including firewood. Ontario gives the same two routes and says the beetles dig galleries under the bark of infected trees and emerge in spring covered in spores.
Forest Research adds that the tree plugs its own water-carrying tissue in reaction to the fungus, which stops water and nutrients moving up the trunk. It also says English elm has suffered the greatest losses because the beetles prefer it to feed on, and not because it is more susceptible than the others.
Symptoms by season as the sources state them
- Early summer. Forest Research says symptoms first appear in early summer: clusters of leaves turn yellow and wilt, then brown, and fall early, and shoots die back from the tips. Ontario and the Canadian Food Inspection Agency say mid-June.
- Late June and July. The Canadian Food Inspection Agency describes wilted upper-crown leaves that curl up and brown by late June or July and often hang on into winter, which it calls flagging.
- Twigs and sapwood. Forest Research says affected twigs sometimes turn down into a shepherd's crook, and that peeling bark from a symptomatic live twig shows dark brown or purple streaks in the outer wood, with a ring of brown staining in cross-section. The Canadian Food Inspection Agency mentions red streaks through the sapwood. Forest Research says the streaking may be missing from some branches, especially lower branches of large trees.
- After the first season. Ontario says leaves on an infected tree fail to develop or stay undersized the following year, and that the disease is usually more widespread inside the tree than the outside symptoms show. It gives death within 1 to 3 years.
Look-alikes
None of the three pages names a look-alike condition for Dutch elm disease. Forest Research does mention a different disease, elm yellows, and says UK notification of elm plant imports exists to guard against it.
When the agencies say a lab or an expert is involved
The Canadian Food Inspection Agency says a trained arborist may need to take branch samples to find out whether an elm is infected. Forest Research describes the twig check above as a way the disease can be confirmed, and says its Tree Health Diagnostic and Advisory Service takes requests for a diagnosis, usually for a fee.
Rules the agencies describe
The Canadian Food Inspection Agency says it is illegal to prune elms during beetle activity in three provinces: Alberta from April 1 to September 30, Saskatchewan from April 1 to August 31, and Manitoba from April 1 to July 31. It adds that elm species should not be pruned anywhere in Canada from April 1 to September 30. It names 2025 detections in the City of Edmonton and the City of Saskatoon and 2024 detections in the Kootenay Boundary Regional District and Edmonton, and says its regulated area was updated to include parts of two British Columbia regional districts and all of Saskatchewan. Its page says moving untreated elm firewood is among the highest-risk ways of carrying the disease into pest-free areas.
Forest Research says certain UK local authorities hold powers under the Dutch Elm Disease (Local Authorities) Order 1984. It says officers may enter land to inspect trees and take samples, and where the disease is present may act themselves or require the owner or occupier to act, usually by destroying the tree.
What the agencies list for management
Forest Research says there is no effective cure and that early sanitation felling, which means removing infected trees and branches, can slow spread. It says fungicides, tree vaccines and chemical or biological controls have limits such as expense, difficulty of application and the need to repeat them, so their use is likely to stay with individual high-value trees. Ontario lists removing dead branches and trees from a site, insecticide against the bark beetles, and fungicide injection for highly valued elms. Who may apply pesticides is covered in the guide to pesticide licences.
Credit
The Forest Research material was read under the Open Government Licence v3.0 and is restated here in our own words. Other agency pages are linked and restated, not copied.