Will the Cold Help Save our Trees from the Emerald Ash Borer?

The invasive and highly destructive, emerald ash borer, is laying waste to ash forests throughout Guelph. Originally from Asia, this distinctive jewel green beetle found its way to the shores of the North American continent in solid wood packaging material on cargo ships in 2002. Since then it has spread throughout the continent and destroyed millions of ash trees in the United States and Canada.

How Cold is Too Cold for the Emerald Ash Borer?

Every organism has a “supercooling point”, the point at which it freezes and dies. A study conducted in China found that emerald ash borer larvae freeze at temperatures of around -23°C. But unfortunately, that applies only to emerald ash borers in China. Similar studies in Canada show that the larvae in Canada can survive temperatures as low as -31oC. This demonstrates how adaptable these beetles are and that the larvae can acclimate to cold weather, allowing them to survive in extreme temperatures. And even if some of the larvae are killed by a sudden severe cold snap, it won’t be enough to halt their advance. ​

How Does the Emerald Ash Borer Survive the Winter?

Emerald ash borers are surprisingly adept at surviving in many different climates and environments, and not even the harshest Canadian winter can stop their onslaught. By spending the winter in the larvae stage, the emerald ash borer can endure extremely low temperatures. And it is these very larvae that are the main cause of the problem. Adult beetles actually don’t do much harm to the ash trees themselves. The female lays her eggs in bark crevices and when the eggs hatch the larvae bore into the cambium layer under the bark and feed on the conducting tissue of the tree, disrupting the flow of nutrients. When spring arrives the adult beetles emerge and the cycle begins again. ​

How to Spot an Emerald Ash Borer

Unfortunately, the emerald ash borer has infiltrated the Guelph area and you need to be on the look-out for signs of an infestation in your garden. It’s not always easy to catch emerald ash borer activity early and one of the first visible signs is a thinning of the tree canopy. This will be above the site of the infestation because the larvae have eaten the conducting tissue of the tree. But by the time you notice, it is probably too late to save the tree. Generally speaking, if more than 50% of the canopy is dead or dying, you will have to remove the infected tree.

​An experienced arborist will be better at identifying emerald ash borer activity than your average gardener. They will look for larval galleries under the bark (S-shaped grooves in the tissue) and small D-shaped exit holes, three to four millimetres wide.

How to Handle an Infestation

Sadly there are no natural emerald ash borer predators in Canada, and while the harsh winter may diminish their numbers, it will not have a significant impact on their survival. This means that human intervention is necessary to protect Canada’s ash trees. The best thing you can do at this point is to:

• Closely monitor the trees in your Guelph garden for emerald ash borer activity
• Have a qualified arborist remove any dead or infected trees as soon as possible and replace them with new trees.
• Wood from infected trees should be mulched (less than an inch square) to minimize the survival of emerald ash borer larvae.

If you suspect the ash trees in your Guelph garden may be infected with emerald ash borer or you want any advice about these pests, you need to contact an arborist as soon as possible. Martin’s Tree Service can help you identify and deal with emerald ash borers in your trees.