Tar spot is commonly found on Tatarian maple trees in Grande Prairie during rainy periods when humidity is high. It causes black spots and blotches on the leaves and samaras of the tree. This disease is only aesthetic, however...it causes no long term harm to the tree.
Prune your maple into an open form to allow good air circulation. This will help dry out the leaves after rain and lower the humidity in the canopy, slowing disease spread.