Right here and now in Calgary there is a behind the scenes battle going on with a tree disease that has preyed on our Elm stands in North America for many years. Luckily we have remained free of Dutch Elm Disease, due in no small part to the hard work done by local professional Arborists and in particular; The Society to Prevent Dutch Elm Disease (StopDED). They work hard to prevent the spread of the disease through public education and the development of policies and bylaws such as the “do not transport firewood” signs at provincial borders, and the provincial Elm Pruning ban which runs from April 1st through to September 31st annually.
You see, the disease is spread by a beetle that bores into the bark of Elm trees. There are three types of beetle currently considered “vectors” . A vector is an organism that carries disease-causing microorganisms from one host to another. Keeping these beetles at bay is key in preventing the spread of the disease. Elm bark beetles, responsible for spreading the deadly Dutch Elm Disease fungus, feed on healthy elms and breed in dead and dying elm trees and Elm firewood and brush piles.
The Pruning Ban
When Elm trees are pruned during the pruning ban period, pheromones are released by the tree which attract these beetles, which are active at this time and will attack an otherwise healthy Elm. This can infect it with Dutch Elm Disease. The disease is serious and spreads quickly, once an elm tree is infected with Dutch Elm Disease it will die, usually within a year. The first signs can be “flagging” in the crown. Flagging is the wilting and deterioration of major limbs in the tree canopy due to damage caused by the disease.
“Flagging” in an American Elm
So you may ask yourself; “Why are they still being sold and planted?”. All you have to do to answer this question is to consider the key points and features of the tree to realize it’s value:
- Above average growth rate
- Stately, cascading form when mature
- Grows well in a wide variety of soils (such as our clay based, alkaline soil)
- Tolerant of drought
- High salt tolerance when planted near roads (road and sidewalk salt can kill some tree species)
- Thrives despite our extreme local climate
- Long Lifespan
What can you do?
There are many things you can do to keep your tree healthy and free of problems such as Dutch Elm Disease
- Keep your elm tree healthy, and properly pruned
- Water throughout the summer, ending in August, water again around halloween or just before freeze up to ensure sufficient soil moisture for the following spring
- Have dead and damaged branches removed properly to reduce breeding sites for the beetle
- Prune only between October 1st and March 31st to prevent pheromone release that can attract the beetles that carry the disease.
- After pruning ensure all Elm wood is disposed of properly through disposal at a landfill or by burning or chipping of the material as the wood is a great place for the insect to re-produce
- Report suspected diseased trees to the StopDED office or contact them via email
If you are concerned about Dutch Elm disease, think your tree may be infected or just want more information regarding the disease feel free to contact us through our website to contact our team of qualified Arborists to help assess your trees needs.