bad maple good maple

What's that white stuff all over these leaves?  It looks like powdery mildew to me.  This is just another reason to hate Norway Maples. These trees have been planted everywhere on PEI. They put out a lot of seeds that spread these trees into native habitat, and their dense shade prevents other plants from growing under them.
These particular seedlings grew from seeds that blew in from my neighbour's place, 150 feet away.  I can always tell Norway maples from any other species of maple, because the Norway is always getting sick.

Here is a Norway Maple with black tar disease, a fungal problem they have been inflicted with here on PEI for many years.

Below is a pic of a Norway Maple leaf with both disesases!

Within a few feet of the sick Norway Maples are two tall, scraggly but very healthy Sugar Maples.

Sugar maples are a native PEI species, but Norways come from - duh - Norway, and are very susceptable to North American disease problems.  They are still sold at PEI garden centres, but are obviously not a good choice.  Other types of Maples are hard to find - you need to go to a native plant nursery such as Sir Andrew MacPhail in Orwell.

Below is a shot of Sugar Maple leaves with no signs of disease.
So how do you tell the two varieties apart?
In the fall, the Norways are usually full of fungal disease.
During the rest of the year, check the leaves.
Norway Maple leaves are wider than they are tall
Other types of maples are longer than they are wide.