Trees infected with emerald ash borer often display distinct signs and symptoms that can help identify an infestation. These signs may not be immediately apparent, as it can take several years for an emerald ash borer infestation to cause noticeable damage to a tree. However, as the infestation progresses, the following symptoms may become more evident.
1. Crown Dieback
One of the most noticeable signs of emerald ash borer infestation is thinning or dieback in the tree's crown (top branches). Dieback occurs as the insects feed on the tree's vascular tissue, disrupting the flow of water and nutrients to the uppermost branches. The crown may also appear thin and sparse, with fewer leaves than healthy trees.
2. Bark Splitting
As the emerald ash borer feeds on the tree's bark, it can create small splits or cracks in the bark. These splits may be visible on the trunk or branches of the tree and may be accompanied by woodpecker activity, as woodpeckers often feed on the insects under the bark.
3. D-Shaped Exit Holes
Emerald ash borer larvae create D-shaped exit holes when they emerge from the tree as adults. These holes, which are about the size of a penny, can be found on the bark of the tree and may be accompanied by small piles of sawdust-like frass (insect excrement) beneath the tree.
4. S-Shaped Galleries
As the emerald ash borer larvae feed under the bark, they create winding, S-shaped galleries. These galleries can be seen when the bark is peeled back to reveal the tree's cambium layer.
5. Increased Woodpecker Activity
Woodpeckers are a reliable indicator of emerald ash borer presence. They will aggressively excavate the bark of infested ash trees to feed on the larvae beneath, often leaving large patches of stripped bark — sometimes called 'blonding.' If you notice unusual woodpecker activity on an ash tree, treat it as a strong warning sign.
Emerald ash borer is now widespread across Simcoe County and Ontario. If you suspect one of your ash trees is infested, contact a certified arborist promptly. Early detection gives you more options — including treatment — before the tree becomes a hazard. If the tree is already heavily infested and structurally compromised, removal is typically the safest course of action.