Tiny tree terrors

A small, green killer is on the loose in southern Ontario. Erin Silverstein of the LEAF program recently spoke to the Scarborough Garden and Horticultural Society about the devastation caused by the Emerald Ash Borer.

The Scarborough Garden and Horticultural Society recently received a visit from a very green guest. Fortunately for them, it was guest speaker Erin Silverstein and not an Emerald Ash Borer beetle.

The Emerald Ash Borer is a tiny metallic green beetle that kills and feeds on all species of ash trees.

Toronto’s approximately 160,000 ash trees make up 8.4 per cent of urban canopy cover in the city.

Emerald Ash Borer: quick facts

  • The Emerald Ash Borer is a beetle that feeds on and kills all species of ash trees.
  • It’s colour is an iridescent metallic green.
  • It is about a centimetre long and less-than-half a centimetre wide.
  • It was first discovered in North America in 2002 in Detroit and Windsor.
  • It is believed to have come from Asia on wood packaging/crates.
  • It flies, but is so small it is often carried by the wind.
  • Most of its spread is by people moving firewood.
  • Ash trees infested by the EAB die within two or three years.
  • Most ash trees in southern Ontario are expected to become infested by 2017.

Source: arbordoctor.net

“This is a huge infestation. It’s all doom and gloom,” Silverstein said. “There is little hope for the ash trees in Ontario. The infestation has spread all throughout Toronto.”

Silverstein said the loss of ash trees is most noticeable in Scarborough and North York, and is most devastating in urban areas.

Silverstein is a University of Toronto graduate and has a degree in forestry and geography, with a deep environmental focus.

She is part of Local Enhancement and Appreciation of Forests (LEAF), an organization dedicated to protecting and improving urban forests since 1996. LEAF has helped plant over 17,000 native trees in the GTA.

It also educates the public about environmental factors that impact the city’s urban forests, including one of Scarborough’s most pressing issues, the Emerald Ash Borer.

The bug has four distinct life-cycle stages: egg, larvae, pupae and adulthood.

But it’s the larvae that causes the most harm.

As they grow and develop, the larvae burrow into the tree’s living tissue that allows nutrients and water to move up and down the trunk, otherwise known as its cambium layer. With thousands of larvae inside, the tree’s vascular system is cut off and the flow of nutrients is interrupted, killing the tree.

“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 1970s and 1980s, decimating street elms, one of the common trees that replaced the Dutch elm was the ash.

Now, Silverstein said the ash will be destroyed as well.

“It’s a bad turn of luck that this has happened,” she said.

Unfortunately, early detection of the infestation is extremely difficult. By the time symptoms, like bark deformities and S-shaped larvae galleries, appear in the tree, it’s more than likely too late to be saved.

“After signs and symptoms appear, it means that the tree is too far gone,” Silverstein said.

However, she added, even though southern Ontario’s ash trees are ultimately doomed, there are ways to prevent the spread of the Emerald Ash Borer into other areas of the province.

How to fight off the beetles

Most of the Emerald Ash Borer’s spread can be blamed 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,” Silverstein said.

A bio-insecticide called TreeAzin can be injected into the base of an ash to kill the beetle and its larvae, but it’s expensive.

The city is using TreeAzin on a case-by-case basis, only injecting 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 said Canadian and American scientists are working on introducing some bio-controls, like a species that would help terminate the Emerald Ash Borer. However, research is in a very early stage.

Silverstein suggested homeowners with infested ash trees should look into removal and replanting. Have a certified arborist test your soils and recommend which type of tree is best to plant in place of an ash, she said.

“When replanting, remember, the bigger the better,” Silverstein said. “Bigger leaves mean more photosynthesis, which increases the canopy cover and ultimately leads to a greener, cleaner environment.”