The Scarborough Garden and Horticultural Society received a visit from a very “green” guest last Tuesday. Fortunately for them it was guest speaker Erin Silverstein, and not an Emerald Ash Borer beetle.
Silverstein is a University of Toronto graduate and has degree in forestry and geography, with deep environmental focus. She is a part of the organization Local Enhancement and Appreciation of Forests (LEAF). The organization has been dedicated to protecting and improving urban forests since 1996 and has helped plant over 7,000 native trees in the GTA.
A large part of this dedication involves educating the public about environmental factors that impact the city’s urban forests. Scarborough’s pressing issue is a pest called the Emerald Ash Borer (EAB).
The EAB is a tiny metallic green beetle that feeds on and kills all species of ash trees. It is believed to have come from Asia on wood packaging, and was initially discovered in North America in 2002 In Detroit and Windsor.
The bug has four distinct life-cycle stages: egg, larvae, pupae and adulthood. Adults feed on the leaves of the ash. They then lay eggs in the bark, which hatch after just a few weeks. A female can lay up to 275 eggs in one year.
There is little hope for the ash trees in Ontario.
— Erin Silverstein
EAB larvae cause the most harm. As they grow and develop, they burrow into the cambium layer of the tree. The cambium is the living tissue of the tree that allows nutrients and water to move up and down the trunk. With thousands of larvae on any given tree, the vascular system of the tree is cut off and the flow of nutrients is interrupted. Thus, the ash dies.
“This is a huge infestation. It’s all doom and gloom,” said Silverstein. “There is little hope for the ash trees in Ontario. The infestation has spread all throughout Toronto.”
There are approximately 160,000 ash trees in Toronto, making up 8.4 per cent of urban canopy cover in the city. Silverstein says the loss of ash trees is most noticeable in Scarborough and North York and is the most devastating in urban areas. Ash trees were readily planted in the past because of their hardiness and ability to withstand harsh environments.
“Most ash trees are expected to become infested and die by 2017,” Silverstein said. “That’s really not that far away. [The beetle] is a fast-moving killer.”
After Dutch elm disease spread through the city in the ’70s and ’80s and decimated many street elms, one of the favourite trees to replace the Dutch Elm was the ash. Now the ash will be destroyed as well.
“It’s a bad turn of luck that this has happened,” said Silverstein.
Unfortunately, early detection of infestation is extremely difficult. By the time symptoms like bark deformities and s-shaped larvae galleries appear in the tree, it is more than likely too late to be saved.
“After signs and symptoms appear, it means that the tree is too far gone,” said Silverstein.
Silverstein says that even though Southern Ontario’s ash trees are ultimately doomed, there are things we can do to prevent the spread of the Emerald Ash Borer into other areas of the province.
Beetles’ range increased by people
Most of the EAB’s spread is to blame on people moving firewood from their homes in the city to other areas of the province. The Canadian Food Inspection Agency has issued Federal Ministerial Orders that prohibit the movement of firewood from specific areas of Ontario. This is to hopefully keep the beetles out of Northern Ontario.
“Let’s try and save cottage country for now,” said Silverstein.
There is a bio-insecticide available called TreeAzin that can be injected into the base of an ash to kill the beetle and its larvae. However, it is very expensive.
The city is using TreeAzin on a case-by-case basis. They will only inject trees that are large and valuable to the urban canopy. Two thousand trees are slated for injections this May. The city plans to remove dead and dying trees on city property, and will replace them with other species.
Silverstein says scientists in Canada and the U.S. are working on introducing some bio-controls, like a species that would help terminate the Emerald Ash Borer. However, this is very early in research.
Silverstein suggests for homeowners with infested ash trees to look into removal and re-planting options. Have a certified arborist test your soils and recommend which type of tree is best to plant in place of an ash.
“When re-planting, remember the bigger the better,” said Silverstein. “Bigger leaves means more photosynthesis, which increases the canopy cover and ultimately leads to a greener, cleaner environment.”
For more information on the Emerald Ash Borer and LEAF’s initiatives, visit yourleaf.org.