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Dutch Elm Disease

Example of Elm tree infected with the DED

Example of Elm tree infected with the DED

Example of Elm tree infected with the DED

Dutch elm disease (DED) is caused by a species of fungus and is considered one of the most devastating tree diseases in the world. The disease is spread by Elm bark beetles who carry the fungus from an infected tree and bore into new Elm trees nearby. It can also be spread via trees’ connected root systems, movement of firewood or contaminated pruning tools. It does not affect trees unrelated to the Elm species.

The fungus blocks the elm’s water and nutrient conducting system. An infected elm tree can die in as little as three weeks or over a period of two to three years.

Waipā District Council has over 250 Elm trees it maintains in parks and streets. Staff will be monitoring and assessing them regularly to identify any trees with the disease early and manage any actions required.

dutch elm disease information sheet

What can you do?

When removing the infected trees, the wood should be immediately chipped and burnt or buried on site or at a landfill site, incorrect processing can spread the disease further. If you suspect DED, please report it to the Ministry for Primary Industries’ (MPIs) Exotic Pest and Disease Hotline on 0800 80 99 66.

Dutch elm disease is a notifiable organism under the Biosecurity Act 1993. If you suspect DED, please report it.

Dutch Elm Disease Standard Operating Procedure

Management of dutch elm disease

There is no known cure for DED-infected elm trees.

Management of the disease includes:

  • Identification of the disease and removal of the infected trees. Wood from felled elm trees should be immediately chipped, burnt or buried on site or buried at a landfill site.
  • Destroying root grafts between adjacent Elm trees before the infected tree is removed.

Symptoms

Symptoms develop quickly within a four-to-five-week period.

Early symptoms include wilting and/or yellowing leaves on the tip of a branch and then turning brown and curling up. The leaves are usually retained on the branch for some time. These symptomatic branches are called flags, and their appearance in an otherwise healthy crown (the branches, leaves, and reproductive structures extending from the trunk or main stems) is called flagging.

As the disease progresses, more flags will appear until the whole crown becomes symptomatic. Other, more diagnostic symptoms of DED include a brown to black streaking or discoloration under the outer bark of infected branches. However, only a trained diagnostician can confirm the presence of DED by conducting specific laboratory tests.

Affected species

Most Ulmus species from Europe and North America are highly susceptible to DED. Some Asian elms and Zelkova have a greater level of resistance.

Spread

The main cause for spread of DED is the European elm bark beetle. Over winter, these beetles as adults or larvae tunnel into elm trees. The fungus that causes DED produces spores in the bark beetles’ tunnels and the beetles may pick up the spores as they move through the tunnels.

The fungal spores are then spread to healthy trees when the adult beetles emerge in spring and summer, fly to healthy trees and feed on the twigs. Infected beetles can also move to new areas in infested timber (especially where the bark is retained) used for furniture, firewood or wood chips.

Root grafts commonly form between closely planted elm trees, especially elms of the same species. DED fungi can spread from diseased trees to healthy trees by these grafts. The fungus can kill an entire avenue of trees in this way.

The disease may be spread via elm nursery stock. Elm flowers (fresh) and bark on timber, chips and handicrafts can also carry the pathogen. It is possible that DED pathogens can be spread on non-disinfected pruning tools.

Vaccination

Council is rolling out a vaccination for Elm trees in Waipā to help protect them against Dutch Elm Disease.

The vaccine will be administered in November on Council parks, reserves and street trees and will extend to privately owned protected trees.

It does not harm the trees, it increases the trees natural defence mechanism and greatly reduces the chances of them dying if they get the disease.

The vaccine is manufactured in the Netherlands. It is currently not available to the public. The vaccination programme is estimated to cost $25,000.

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