Question
I have two vine maple trees that have yellowish brown spots spreading all over the leaves. I'm not sure how old they are but they're only about 6' tall. They also have what looks like some kind of moss growing on the bark. I'm in the Northwest. Washington state to be exact. They don't to happy either. They are leaning a bit. How do I treat this? Please help! :)

Answer
Sounds like lichens. When lichen is wet from rain or dew, it grows actively. It also likes sunshine, and will grow well in winter after the leaves have fallen from deciduous trees and no longer block the light, or on trees with badly thinned canopies.

If you have lichen growing on the trunks or branches of your trees or shrubs, don't panic. Lichen will not actually harm your trees. That's because it takes its nourishment from the air rather than from its host. Lichens are often blamed for the decline and death of shrubs and trees because they are commonly found on dead branches and limbs. In actual fact, exposed limbs on damaged plants simply give lichens access to the sun they need for growth with little competition. There is no need to do anything, as lichen is not detrimental to the health of your plants.
The lichen will not effect the health of the tree.
If you feel you must do something and do not want the lichens on the trunk you might try this. No products are labeled for lichen control, but copper fungicides labeled for ball moss, or the home remedy of baking soda (sodium bicarbonate) for ball moss control (label pending) are detrimental. In pecan orchards, the fungicides used for scab and downy spot control reduce lichen numbers due to their effects on the fungal partners in lichens. However I would leave the lichens be.

The effect of lichens on a tree are only slightly detrimental. The plants are epiphytes. That is they derive their nutrients from the air and not from the plant on which they are growing. Although they are not parasitized, literature reports suggest that lichens do have a slight negative effect. The main concern is that lichens give a tree an unkept appearance. Presence of lichens also is a good indicator of a thin tree canopy. This often leads homeowners to conclude that lichens are the cause and not the effect of thin foliage. The best control for lichens is maintain the tree in good condition. This will insure a dense canopy which will shade the limbs and reduce photosynthesis. Without photosynthesis, lichens are not able to manufacture food needed for growth and development.  

The baking soda recommendation I have heard of is 40 pounds of baking soda per 100 gallons which comes to 0.4 lb of baking soda to 1 gal of water. But I would not do anything about the lichens but I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. this will increase the overall health of the tree.