What’s small, green, flies and is less than an inch long? Not sure? It’s beautiful to look at, but it has a devastating impact on the ash trees around us? That’s right, it’s the Emerald Ash Borer – or EAB as its ‘friends’ like to know it!

EAB is a non-native insect to North America. It likely found its way here from its native homelands in Asia via shipping pallets and containers and was first discovered in Michigan in 2002 and the same year across the border in Ontario – although may well have been here for a decade or more. Despite best efforts, over the past 14 years, EAB has settled in quite nicely and left a trail of destruction in its wake.

Moving through south western Ontario and now firmly resident in Halton, EAB is a winged insect found in late summer. The winged stage is the adult and as an adult, is little more than a striking bug seen amongst the trees and feeding on the leaves of ash. However, it lays eggs exclusively on ash trees – and its good at finding them in a forest – and its children are the concern. Once hatched, the EAB pupae start to eat the layer of material between the woody centre of the tree and the outer bark and create a network of galleries or channels through the tree. These in essence ‘ring bark’ the tree and prevent the vital upward flow of water and downward flow of nutrients, starving the tree. By the time the EAB eggs are laid, the trees fate is established and the impacted ash will die – in as little as a season and at most over 3 – 5 years. Did we say EAB was good at finding ash? It is and its also good at killing them – 98% of ash in an area will be impacted, and the mortality is greater than 99%.

Infected Ash Tree

Present In Halton since 2011 (if not earlier), the impacts are readily seen to even the untrained eye. Moving through the watershed this summer those stark, dead trees lining roads, trails and the escarpment – most likely ash. In some municipality owned woodlots where ash was the dominant tree in a park woodlot, entire woodlands have been removed. Across the mixed woodlands of the escarpment backdrop of Halton, ash makes up between 7% and 15% of the tree canopy on average and makes a visible dead component to our forests now. Over the next 3 – 5 years we can expect mortality to increase as most ash become impacted.

So what’s the problem? Well, one thing is for sure – when any tree starts to grow, it will, at some point die and fall over. In a ‘normal’ forest system this is a balance – trees die and are either removed before they fall over – for example, to protect a building or a trail – or they die and fall in the forest and are rapidly replaced. EAB is exaggerating that a causing a tidal wave of dead trees that is growing over the next few years. Conservation Halton estimates that over the next 10 years on its property alone, and only focusing on areas where a tree has potential to fall on something (trail, building, parking lots etc), there are more than 50,000 trees that will be impacted.

And ash trees are good at regenerating – so what’s growing where the ash fall down? You guessed it, more ash. So while early estimates hoped that after a ‘wave’ of EAB, woodlands would be allowed to recover naturally without EAB, the evidence from the south west of Ontario indicates that EAB does not leave, but simply reduces in volume as the amount of ash is less and smaller in size. It looks like it’s here to stay.

What can we do? We hope that there are solutions. Immediately, we are treating some trees with a chemical injection that prevents EAB from feeding on the tree. Its expensive, and so only a few 100 trees can be treated, but with luck, these will provide a seed source for the future re-establishment of ash. And the rest – well, there’s not much that can be done apart from remove them before they present a risk to the public. On a wider scale, there are natural inspects that prey on EAB in its native Asia and scientists are looking into the possibility of introducing them here to prey on it here… but that’s a risk in itself – we have to be careful that when the prey is introduced, it does not find something more attractive, tasty and native to Ontario to eat than the invading EAB and create an even bigger problem. So, we should be ready for EAB to be a big deal in our woodlands for the next few years.

Its not great news for sure, we are lucky that our woodlands are healthy, well managed and diverse. We will see a dramatic decline in ash, but the woodland and forests will continue to exist as other species continue to thrive. EAB only impacts ash trees. Its not the only bug out there that kills trees … but thankfully, at the minute it’s the only one we have to contend with!

How can you help? Keep an eye on your ash trees to watch out for signs:

  • The leaves in the top third of the ash tree lose their green colour, thin and die back.
  • White lines or galleries are evident under the tree’s bark.
  • The bark begins to split.
  • There are small D-shaped holes in the bark. (This is from the larvae tunneling through the trunk)
  • New growth or shoots of leafs are present at the base of the tree
  • The bark has large whitish looking patches where squirrels and birds have scratched away the top layer to get at the insects underneath.

Most important of all is to not move wood around; the EAB pupae can still be in wood such as fire wood, and EAB has not spread everywhere in Ontario – preventing its spread is key and so remember to not move wood between places – so no taking camp wood with you on the next camping trip, and please don’t take fire wood with you to the cottage.

If you want to learn more on how Forestry at Conservation Halton is monitoring and proactively managing the ash population on its property, please visit our website.


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Last modified: September 5, 2017

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