my maple tree has brown spots on the leaves can you tell me why this is?

This sounds like a fungus disease. If you are not finding insects and you are finding this spotting all over the tree you are deffinitly looking at a blight. It can be a variety of different blights but it will not hurt your tree. YOu should be able to pick up a fungicide that will kill this disease. You will want to watch the disease over the years as most fungal disease require multiple treatments. Many people make the mistake thinking that theywill cure there tree in one shot.

The Arbor Doctor

The spots may be a leaf spot fungus which infects the leaves. This fungus normally does not effect the overall health of the tree but will make the leaves drop prematurely. The control for this disease is to spray the leaves in the spring with a fungicide. Raking up the leaves this fall and destroying them will greatly reduce the spore from the fungus and cut the infection down for the next year.

Most fungi infect in spring as leaves are unfolding, once symptoms are visible on the leaves it is too late for chemical control. You may need to call a professional to be sure and help correct the problem.

This is a little bug (sorry I don't know the name) that bites the leaf for liquid. It won't hurt the tree.