Is the tree healthy?

Look for sparse leaves or dead and dying branches in the upper part of the tree - it may be easier to see this by standing back from the tree. If there is more than 20% loss of leaves (also called dieback) it is not healthy enough to be treated effectively. Also look for shoots growing from the base of the tree. If present, these are symptoms that the tree is stressed or declining, either from emerald ash borer (EAB) or another stressor, and is not a good candidate for treatment.

Ash tree with thinning leaves and branches from emerald ash borer attack. Image: Chris Gynan, Silv-Econ Ltd.

Is the tree structurally sound?

Look for any wounds or areas of decay on the tree's trunk, or large sections of dead branches - these findings indicate that the the tree could fail for structural reasons. Trees that are leaning at a pronounced angle may also fail. Trees that are not structurally sound are not worth treating with insecticide.

How big is the tree?

Smaller trees are often more economical to remove and replace than to treat with insecticide. Measure the circumference of the tree at chest height (1.3 metres above the ground) and multiply the measurement by 0.32 to calculate the diameter. If the tree is greater than 20-25 cm in diameter at chest height, it is of a reasonable size to consider treatment.

Does the tree have any signs or symptoms of emerald ash borer attack?

Check the tree for signs of EAB activity. If there are woodpeckers feeding on the tree, or there are large areas of peeled bark or feeding holes, this means that the tree is probably already infested by EAB. Other signs of EAB infestation include splitting of the bark on the tree's trunk or branches, or exit holes in the bark. Trees with any of these signs are not good candidates for treatment.

More on signs and symptoms of EAB infested trees.

How important is the tree to you?

Only you can put a value on your ash tree. Does it have sentimental or aesthetic value to you? Does it provide shade or privacy, or buffer noise or wind? If so, it may be of more value to you to treat the tree.

LEAF's tree benefit estimator allows you to calculate the environmental benefits of your tree.