Gardening and Horticulture - Trying to save our old sick tree

Dear experts, I am looking for advice to save our old tree. We have been in this location for a couple of years and each year I have seen this tree getting worst.
This year it has not gotten as green as the tree next door. I see the evidence that some branches that have been trimmed a long time ago. I have made sure I water this tree every other day. I also have put a few fertilizer sticks around it this year and last year.
The only thing I did this year that might be an issue is I sprayed an area 10 feet away from the tree with weed killer spray.
I realize now that the root of this old tree must be spread all around and the spray I used might have damaged it.
Is there anything I can do to help this old tree?

Thanks.

P.S. I have included some pictures to show the black dots on the leafs. http://farid.fatourchi.com/Tree/

Best bet is to drill a bunch of holes (30-40) around the tree using a small augur. Fill these with gravel. the grass will cover the gravel. This allows water and fertilizer to reach the roots. The term is vertical mulching. Check out this web page
http://www.bloomingarden.com/verticalmulch.html


BTW - you're doing more harm than good watering like you are. You are encouraging the roots to grow at the surface. Give them a good soak of an inch twice a week. That way, the way the water goes deep into the ground.

Overwatering can cause wet feet that causes silver maple to be more susceptible to bacterial disease and blight. These trees are fast growing, have weak wood, a shorter life span than other maples, and prefer poorer soil and drier growing conditions. If the tree is a prized specimen in your landscape, consulting with an arborist is recommended to diagnose health issues and to determine the best care and maintenance for your silver maple.

thank you all for your comments.