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Emerald Ash Borer in London, Ontario

With winter upon us, we anticipate fallen leaves and bare branches, but this year you can also expect to see the leaves and trees themselves coming down for an entirely different reason. As the city continues to do battle with the insidious Emerald Ash Borer (EAB), London’s ash causalities are piling up.

The following provides an introduction to the borer, information on identifying ash trees, and ways to treat infestations.

The Emerald Ash Borer

The war against EAB is not new. In 2002, the Canadian Food Inspection Agency detected the evasive insect. Its North American origin is believed to be Detroit/Windsor and it is thought to have been introduced accidentally on wood pallets from Asia.

The adult EAB is actually quite harmless, feeding lightly on foliage. Most of the damage is a result of the feeding larvae, the insect's young. The tiny white larvae gouge paths through the cambium, the layer just below the bark that transports nutrients to the rest of the tree. By cutting off nourishment, the young borers slowly starve the tree to death. Once mature, the adult beetle exits the ash tree by boring a tiny, “D” shaped hole. These holes are sure signs that the Emerald Ash Borer is present in the tree. In some cases, additional round holes may also be found where hungry woodpeckers have tried to get to the larvae living under the bark to eat.

The 10mm insect will wipe out nearly all of London’s ash trees over the next 7-10 years. Depending on the level of infestation, each affected tree could be dead within a year. (In less severe cases, it can take up to five years for EAB to kill a healthy tree). London has over half a million ash trees - 10% of the entire local tree population – so the impact to our urban forest will be substantial.

The EAB is mobile and there is evidence of the destructive critter all across London - with the greatest concentration in the city's north and east. (R1) Trees that have been damaged by the borer will stop producing leaves and limbs will become brittle.

Saving London’s Ash

Trees on public property are being examined on a frequent basis by city employees for evidence of EAB. In many cases, trees affected by the emerald ash borer or those at high risk of attack are removed to eliminate spread to nearby trees.

Municipally contracted workers have already begun to remove ash trees from the public landscape. When all is said and down, roughly 10,000 ash trees that currently line the streets and dot parks will be cut down by the City of London. (R7) This does not count the tens of thousands of additional ash trees in city-owned woodlands, and the hundreds of thousands of trees on private property.

Currently, the only effective weapon in the fight is TreeAzin, a bio-insecticide that enters the tree via injection into the trunk. Trees administered TreeAzin have increase likelihood of surviving, killing more than 95% of the active larvae and reducing egg production in surviving females(R4). The City of London has identified 384 large trees that it hopes to save using the chemical (R7).

Identify Your Ash

Ninety-eight percent of ash trees are found on private property - a whopping 430,000 within the City's Urban Growth Boundary, and over 200,000 outside the Urban Growth Boundary - prompting the city to seek help from homeowners in suppressing the bug (R5).

Ash trees are identified by opposing branches bearing compound leaves that have slightly toothed margins. Each leaf typically consists of 5-11 spear-shaped leaflets. Mature ash trees have rough bark that resembles a diamond pattern. Younger members of the species have similar traits, but the bark is much smoother.

There are some species with similar distinctions and homeowners should be aware of the differences before acting. More information can be found online at the Ash Tree Identification Guide.

What You Can Do

Homeowners are encouraged to assess their trees and determine the level of infestation. Early detection and treatment with TreeAzin could save the tree. If a tree is already dead or will inevitably die, it is recommended that it be taken down to avoid potential hazard to persons or property. The signs of EAB include leaves dying back in the top third of the tree, branches growing from the trunk or root, the bark begins to split revealing serpentine "S-shaped" tunnels, and the distinctive D-shaped exit holes (R1b).

Yard waste instructions are outlined on the City’s website to help with mitigation. Ash material, excluding firewood, may be set-out at the curb for your scheduled yard waste collection week. There are restrictions on ash waste travelling beyond the city limits. Details on how to handle materials are found in the Waste Reduction & Conservation Calendar or by visiting the City of London’s webpage. DO NOT MOVE ASH FIREWOOD OUT OF THE CITY! Transporting firewood from an EAB infested area to other areas quickens the spread of the EAB, and can cause the death of thousands of trees that may otherwise have been candidate for saving.

The Emerald Ash Borer Strategy is a 2011 report commissioned by the City of London. The document, prepared by Davey Resource Group, was released in September 2011, and confirms most of the details surrounding the threat of the EAB to London’s lush canopy. Through a combination of treating, removing, and replanting, the report insists that London can actively pursue measures to eliminate the borer and protect its status as the Forest City.

The report, details about the EAB, and much more can be found on the City of London website here.

Article written by Brandon Watson.

Reference and additional links

R1 – City of London – EAB Info

R2 – Canadian Food Inspection Agency – EAB Fact Sheet

R3 – Canadian Food Inspection Agency - Symptoms of EAB

R4 – City of London – Protecting Ash Trees on City Owned Property

R5 - BioForest (TreeAzin)

R6 – Ash Tree Identification guide

R7- London Free Press, Jan. 13, 2012

Emerald Ash Borer Information and Research

Video series by LEAF on EAB

Emerald Ash Borer as an adult

Fast Facts about Emerald Ash Borer

The City of London is removing trees that have died or will die as a result of the EAB. If left, they would become brittle and hazardous to the public. Ash makes up roughly 10% of London’s tree count. (R4)

The city has implemented a bi-annual treatment of at-risk trees that will protect them from infestation. With the vast majority of ash trees residing on private property, the challenge for the city is to reach those areas. For more information, citizens can contact 519-661-2500 ext. 2339 or emailing eab@london.ca. (R4)

The greatest damage is done by the EAB larvae, which attacks the nutrient layer just below the bark effectively starving the tree to death. (R3)

Although your tree may have some signs of EAB infestation, other diseases/infestations may be affecting your trees growth. It is recommended you have a certified arborist inspect your tree before you begin treatment. (R1b)

Ash leaves are compound, opposite, with 5-11 leaflets on each leaf.

The adult insect tunnels out of the tree, leaving damage under the bark and a "D" shaped hole.

TreeAzin, shown being applied above, is the only effective means of saving an ash tree from the Emerald Ash Borer.