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What is Dutch Elm Disease (DED)

Dutch Elm Disease (DED) has devastated Manitoba’s native American Elm tree population since its arrival here in 1975. Dutch elm disease is a fungal disease that blocks water movement in elm trees and eventually leads to the
death of the entire tree. A dead or dying elm attracts elm bark beetles, which breed underneath the bark of the tree. Beatles emerging from trees killed by Dutch elm disease are contaminated with the spores of the fungus and spread them to other elms to feed or spend the winter. Although more resistant than the American elm – Siberian elms can still become infected and not only help the disease spread to more trees – but also die as well.

Sign and Symptoms

Trees may produce 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.


Watering & Fertilizing

Prevention - What you need an arborist to do


  • Prune dead or dying branches immediately.
  • Pruning restrictions in the Dutch Elm disease act
    prohibits pruning elm trees between April 1 to July 31 (Winnipeg).
  • It is illegal to store or transport elm wood for any
    other reason than disposal at a landfill designated to
    receive elm wood.

Basal Spray

  • Controls elm bark beetles, the carriers of Dutch Elm Disease, by spraying insecticide onto the lower 50 cm of elm trees.
  • This is done in late summer/fall.

Therapeutic Injection

  • Fungicides Arbotect® 20-S are injected directly into elm trees to prevent the DED fungus from growing in the tree.
  • Injections should be performed by licensed injection specialist in order to obtain effective results.
  • The procedure is most effective when leaves reach full size.
  • This treatment needs to be repeated every few years.

Insect Control

  • Repeated defoliation by defoliating caterpillars will weaken the tree making it susceptible to DED. Early treatment by spraying the leaves of the tree in early spring with an environmentally friendly product (BT) can prevent this.
  • Tangle foot banding: Although this is still a widely used method of control for Cankerworms. Unfortunately, it is ineffective for other defoliators, such as Bruce Spanworm, and does not prevent migration from un-banded trees. In most cases, banding will only control a small percentage of defoliators.
Stain on twig with Dutch Elm Disease
Flagging leaves of early Dutch Elm Diseased elm tree
Crown Condition of a Dutch Elm Diseased Tree

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