I live in the east end of Toronto, near the lake. My tree is on the front lawn and although it is on the north side of the house, it gets a lot of sun. These discolourations started appearing a couple of weeks ago – am unsure what to do about it. Can you help??
Unfortunately, it appears that your tree has Anthracnose, a fungal foliar disease that often affects shade trees. The good news is that other than how unsightly the leaf damage is, it is rarely a serious problem for the tree.
There are several kinds of fungi that cause this disease. Cool, wet weather in spring contribute to the release of spores that have overwintered in fallen leaves. The spores are spread by wind and rain causing spots to develop along the leaf margins. These expand outwards and younger leaves can shrivel and die.
Here is a link to a Toronto Master Gardener answer that provides more information about Anthracnose:
The Morton Arboretum and Michigan State Uninversity are other good sources for information on this disease: