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Dutch Elm Disease - Frequently Asked Questions

 

About this FAQ

This page contains a selection of frequently asked questions (FAQs) about Dutch elm disease in Manitoba.

 

Contents:

 

Elm Tree Identification

Q. What does an elm tree look like?
A.
Elms are vase or umbrella shaped with rising branches from a single trunk. The have dark green, veined leaves that are toothed and uneven at the base. The bark is dark grey/brown and furrowed, with broad intersecting ridges and a rough flaky appearance. In cross-section the bark has alternating brown and white layers.



Dutch Elm Disease

Q. Which trees get Dutch elm disease?
A.
The native American elm is most susceptible to Dutch elm disease. The introduced Siberian elm species (sometimes incorrectly referred to as Chinese elm) is less susceptible to Dutch elm disease, but can still become infected and die.

Q. What is Dutch elm disease?
A.
Dutch elm disease is a fungal disease that blocks water movement in elm trees and eventually leads to death of the entire tree.

Q. How can I tell if my elm has Dutch elm disease?
A.
Trees may produce small sparse leaves in spring. In early summer, you'll notice a sudden wilting of leaves, usually at the top of the tree. Leaves curl and turn brown but do not fall from the tree. In late summer, leaves may become yellow and fall prematurely. Symptoms can spread quickly throughout the tree. Infected branches often show a brown stain on the wood, which can be seen by peeling back the bark. Note: If testing your own tree, sterilize your cutting tool after each cut to prevent spreading the Dutch elm disease fungus to other trees.

Q. How long does it take for Dutch elm disease to kill my trees?
A.
Young, vigourous growing trees can be killed in a few weeks, whereas larger, slower growing trees can take one to two years.

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How the Disease Spreads

Q. How is Dutch elm disease spread from infected elms to healthy elms on my property?
A.
A dead or dying elm on your property attracts elm bark beetles, which breed underneath the bark of the tree. Beetles emerging from trees killed by Dutch elm disease are contaminated with the spores of the Dutch elm disease fungus. When these infected beetles mature and move to other elms to feed or spend the winter, they continue the infection cycle.

Q. What does the native elm bark beetle look like?
A.
The adult beetles are tiny, dark brown, and not easily visible to the naked eye. (actual size of 2-3 mm)


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Prevention and Control of Dutch elm disease

What can I do to prevent Dutch elm disease from infecting my healthy elm?

  1. Get rid of all dead and diseased elm trees and elm firewood.
  2. Basal spray healthy elms with insecticide to kill elm bark beetles, which spend the winter in the bark at the base of the tree.
  3. Keep elms in healthy condition through proper tree care (pruning, regular watering and fertilization).
  4. Inject healthy elm trees with a registered fungicide.

Q. How should I dispose of elm wood?
A.
Dead or dying elm trees can be removed entirely any time of the year. Elms should be cut flush with the ground and either burned, buried, or chipped. Contact your city, town, or RM office for on-site burning regulations and for the location of the nearest disposal site.

Q. Can I keep elms as firewood?
A. No. Using elms as firewood, a major factor in spreading Dutch elm disease, is illegal.

Q. Why should I basal spray my elm trees and how is it done?
A. Basal spraying refers to spraying the bottom .5 metre of the trunk of all your elm trees with an insecticide containing "chlorpyrifos." This prevents the overwintering of elm bark beetles, which may be carrying Dutch elm disease fungal spores. A 0.5% chlorpyrifos solution should be thoroughly sprayed into the cracks and crevices and around the root flare. Apply any time during August or early September and reapply every two years.

Q. Where can I purchase the chemical used to basal spray my elms?
A. Basal spray chemicals can be found at local nursery/garden centers and hardware stores. The chemical must contain the active ingredient chlorpyrifos. Trade names to look for include Banisect (Green Cross), Chlorisect and Solgard (CIL) and BugCan-C Lawn Insect Spray (Later's).
Note: The registration of chlorpyrifos was recently changed. Contact your local dealer for current application restrictions and available products.

Q. What are those "sticky bands" I see wrapped around tree trunks? Do they control Dutch elm disease?
A. They are tanglefoot bands that prevent spring and fall cankerworm wingless female moths from crawling up the tree trunk to lay eggs. Cankerworm feeding can cause severe defoliation which stresses and weakens trees. Reducing the stress on trees makes them less attractive to elm bark beetles. Tanglefoot bands may also play an incidental role in trapping a few bark beetles.

Q. My tree has sap leaking from the trunk and staining the bark. Is this a sign of Dutch elm disease?
A.
This condition, known as wetwood or slimeflux, is fairly common in elm trees. It is not Dutch elm disease related. It is caused by bacteria and is more unsightly than harmful to the tree. Usually it occurs at a pruning wound or at the junction of two major limbs.

Q. Can Dutch elm disease be pruned from my elm tree?
A. No, Dutch elm disease cannot be pruned out of the tree.

Q. When can I prune my elm tree?
A. You can prune healthy elms to remove dead or damaged branches anytime except between April 1st and July 31st. During this time beetles are active and would be attracted to open wounds which makes your tree more vulnerable to Dutch elm disease.
Note: It is important to sterilize your pruning tools between trees.

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Q. What are elm tree injections?
A. Fungicides are injected into the root flare area of healthy elms to prevent the Dutch elm disease fungus from establishing in your tree. Although tree injections are expensive and must be repeated every few years, injections can be an effective preventive treatment of Dutch elm disease. Injections are most effective when the leaves reach full size in early summer. Injections should be done by a professional tree care service to guarantee proper application procedures. Several fungicide products are registered for elm tree injections.

Q. Can you save an infected elm by injecting it?
A. Injections are used primarily as a preventive measure but may arrest the disease in trees showing very early symptoms. Injection should be accompanied by proper pruning of the diseased branches.

Q. Can you recommend a company to spray, prune and/or inject my elms?
A. The Government of Manitoba cannot recommend a specific company, so please look in the phone book under Tree Service. Ensure that the company you select employs licensed and insured arborists/tree pruners.

Q. Is assistance available to remove dead/diseased trees?
A. A number of communities have entered into a cost-sharing agreement (CSA) with the Government of Manitoba. Under these agreements a number of services are offered, including identification and removal of dead and dying elms at no cost to the homeowner. Cost-sharing agreement communities perform basal spraying of public elms, tree pruning and tree replacement. The Government of Manitoba also maintains a buffer zone around the city of Winnipeg to reduce the disease pressure on the city's elm trees. Assistance is available to property owners who require information about identifying elms, Dutch elm disease symptoms, and prevention and management methods.

Q. I have a tree which is tagged for removal in my yard. When will it be removed?
A. For further information about tree removal call:
In the City of Winnipeg - Urban Forestry Department - 311
In Brandon - Parks Division - 204-729-2148
Outside Brandon and Winnipeg - 204-945-5006

Q. Is there a cure for Dutch elm disease now?
A.
No. Research is being done to find an effective, cost-efficient treatment and to develop resistant varieties of elm.

Q. Whom do I call if I suspect my elm tree has Dutch elm disease or for more information on Dutch elm disease?
A. In the City of Winnipeg - Urban Forestry Department - 311
In Brandon - Parks Division - 204-729-2148
Outside Brandon and Winnipeg - 204-945-5006
email - treecare@gov.mb.ca

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