Q&A: Birch tree sounds like it has Birch Borer
What do I do now that we are not able to use pesticides in Ontario? Any suggestions?
A. Having researched the problems with birches and coming to the conclusion that you may have a European Birch 'Youngii" or Betula pendula "Youngii" I discovered that although this ornamental tree is quite beautiful with lovely yellow fall colour, it a tree that requires more maintenance in the form of spraying than other trees in the birch family.
The tree has a history of being succeptible to the Bronze Birch Borer which bores its way into the sapwood of the tree, lays eggs in the trunk or branches in August and goes through four instars (stages) over a period of two years and then exits leaving a "D" shaped hole in a six week period beginning in June and ending in July. The tree will have swollen areas of the trunk and leaves will be chloric or yellow and the foliage in the upper crown of the tree.
I would have to say that only a certified arborist could make the final diagnosis of your tree. Having done that, the arborist would then know what treatment could be made to your tree. The arborist would have a license for treating your tree.
Find a certified arborist near you on the Landscape Ontario Find a Company page here. I hope this answer helps you.
Lake Simcoe South Master Gardener