Pests image: Dutch Elm Disease (DED)


Dutch elm disease is caused by two strains of an aggressive fungus (Ophiostoma-ulmi Ophiostoma-novo-ulmi) that provoke elm trees to die regardless of their health. It is considered the most costly shade tree disease and will remain active in a community as long as there are susceptible trees. The fungus invades the water transporting vessels and produces toxins to which the tree reacts. In defense to the toxins, the tree produces tyloses designed to block the spread of the fungus. The combination of the toxins and the defense mechanisms of the tree inhibit water flow to the crown, which causes wilting and tree death.

Female elm bark beetles lay their eggs beneath the bark of dead and dying elm trees. If the elm is infected with Dutch Elm Disease, the newly hatched beetles will emerge from the tree carrying the deadly fungus on their bodies. The beetles fly to healthy trees to feed on 2–4-year-old branches, and thereby spreading the disease.

Dutch elm disease can also be spread by root contact/root grafting from one diseased elm to a healthy elm.

Sign and Symptoms

Dutch elm disease symptoms begin to develop 4–6 week after infection. The first noticeable symptom that results from the fungal occupation of the water conducting vessels is wilting or “flagging” of one or more branches, usually starting at the branch tip. Leaves on infected branches turn dull green to yellow, curl, and become dry and brittle. As the infection spreads, the wood beneath the bark displays a brown discolouration.


Most elm tree species are susceptible including American Elm

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Dutch elm disease is difficult to control and, without proper management, it will wipe out a large population of elms in just a few years. However, with a properly implemented management program, the devastating effects of the disease can be greatly reduced.

An effective Dutch elm disease management program includes four parts for control:

  1. Rapid detection and rapid removal of diseased elms
    • A tree inventory and monitoring program are the foundation. Early detection and rapid removal can keep mortality just under 2%/year, and without treatment, there is no certainty of which elms will become infected.
  2. Disruption of root graft transmission
  3. Saving diseased elms (Tracing)
  4. Protecting high-value elms with Arbotect 20-S

Treatment should be used in conjunction with an insect control and sanitation program (early detection and rapid removal of infected trees) in order to obtain best results. Use of Arbotect 20-S does not prevent the transmission of Dutch elm disease via root grafts.

Applications can be made after leaves have fully flushed in the spring. Treatments can continue throughout the growing season, or until leaf senescence in the fall.

One application of Arbotect 20-S protects the entire tree for up to three years yielding significant cost savings.

Multi-year control prevents transmission by elm bark beetle at peak flight times early in the growing season. To protect a tree from a beetle-transmitted fungal infection, Arbotect 20-S must be evenly and completely distributed throughout the two to four year old branches.

To ensure even distribution, Arbotect 20-S is injected using the Macro-Infusion injection method. Macro-Infusion injects a large volume of solution into the root flares of the tree. This solution is then transported throughout the canopy providing a protective fungicide barrier.

Only Arbotect 20-S has the ability to move into the newly formed sapwood, while resisting degradation resulting from cold, heat, and other adverse conditions. Arbotect 20-S was first registered over 30 years ago and has a proven 99% success rate when applied as per manufacturer’s directions.

Protecting Elm Trees Using Arbotect 20-S

Arbotect 20-S is a preventative treatment for Dutch Elm Disease (DED). It is the only scientifically proven systemic fungicide that provides multi-year protection (up to 3 years) from DED, with a proven success rate of 99% when included in an DED IPM program.

Featured Treatments

Map Arbotect 20-S Fungicide

Arbotect 20-S Fungicide

Arbotect 20-S is a systemic fungicide formulated with Thiabendazole and is applied through a process called macro-infusion. Arbotect 20-S is the only scientifically proven fungicide that provides multi-year protection from Dutch Elm Disease.

In Canada, Arbotect 20-S is registered by Health Canada’s Pest Management Regulatory Agency (PM...