Dutch Elm Disease is a fungus that spreads through the conductive vessels of an elm tree. The vessels become blocked, and branches in the canopy quickly begin to die. The disease spreads easily as elm bark beetles inadvertently carry spores of the fungus from tree to tree as they feed. Elm bark beetles are attracted to the pheromones that stressed trees emit. DED can also spread underground if the roots of an infected tree have grafted to another elm.
HOW DO I PREVENT DED?
Dutch Elm Disease is an ongoing problem in Winnipeg, and it is one that we must not lose sight of amongst the upcoming threats to our urban forest. Maintaining healthy trees is vitally important in preventing DED in addition to preventative treatment.
- Preventative Injection treatment. This is a fungicide treatment that prevents the disease from spreading within the vessels when spores are introduced to the tree. Preventative treatments are repeated every three years. They are administered by knowledgeable, experienced arborists who also possess a Manitoba Pesticide Applicators Licence.
- Care for your trees.
- Regular maintenance pruning (every 3-4 years) to remove dead branches will help your trees conserve energy and reallocate it to growth or defense. Keeping your trees free of dead branches also reduces how beetles are attracted to your trees.
- Regular watering during dry periods and just before freeze-up will enable your trees to thrive. Every living cell in your tree needs water to function properly. When trees do not take up enough water, energy production in the leaves decreases and the tree’s internal defense mechanisms become restricted. For tips on watering, click here.
- Prevent defoliation from caterpillars or worms. Trees emit a stress hormone in reaction to the worm feeding, which can attract the elm bark beetle. When trees lose their canopy, they use stored energy to re-grow leaves, and they rarely restore the canopy as it was before. This makes identifying symptoms of DED very difficult. If defoliation occurs in consecutive years, the tree’s energy reserves will become depleted. The tree will not be able to defend itself during other stress factors such as drought or invasion of decay organisms. Call Trilogy Tree Services in May and June, for help with BTK spraying.
- Look Up. Symptoms of DED begin to show at the end of June or beginning of July. Make sure you are constantly checking your trees for symptoms of pale, wilted looking leaves. If you spot anything suspicious, call our arborists immediately for diagnosis. Once infected, the disease spreads quickly and a tree could become untreatable within a week.
- Remove diseased elms that are near a healthy tree. Although the City of Winnipeg will remove any diseased elm on public or private property, they may not get it done in time. Diseased trees should be removed in the fall and winter before beetles take flight in April. If a diseased tree is still standing at the next growing season, beetles emerge from it and carry the fungus to the next tree. Also, as the fungus progresses through the tree and into the roots, it will pass through root grafts and infect the neighbouring tree. Removal of a diseased tree may be the cost of saving the next one.
- Follow the Provincial DED Regulations. Do not prune elms between April 1st and August 31st, and do not store elmwood on your property. Link to DED regulations
MY TREE LOOKS DISEASED, WHAT SHOULD I DO?
Contact the arborists at Trilogy Tree Services immediately. If symptoms are noticed at the onset of infection, treatment may be possible. Treatment involves pruning out the diseased section of the canopy in conjunction with fungicide injections.
Treating diseased trees requires a high level of knowledge and experience. Our arborists have gained knowledge from the two individuals who pioneered fungicide injections in Manitoba. Our arborists will bring the required skills, and determine if your tree can be saved.
HOW DO PREVENTATIVE INJECTIONS WORK?
Using specialized equipment, the fungicide is injected into the root flare of the tree. Choosing the correct number and locations of injection sites on an elm tree is crucial for uniform fungicide distribution in the crown. As the tree pulls water up to the tips of the branches, it also moves the fungicide throughout the canopy. The fungicide moves up from point of injection, therefore it is not possible to get fungicide into the root system. This is why infection through a root graft is fatal.
Trilogy Tree Services has a dedicated team of arborists that inject elms during the optimal time frame of July and August. Treatments remain effective for three years. The cost of this treatment is based on tree size.
DOES BANDING MY TREES PREVENT DED?
No. Banding your trees will aide in reducing cankerworm defoliation. Cankerworms are the only harmful insect a tree band will control, unfortunately, many beneficial insects also get stuck to the band. Tree bands offer limited control because once the band is covered with insects or debris, the moths are able to crawl over it. Spraying the tree with a biological product such as BTK provides more effective control, that is still environmentally friendly.