Question
I live in South Eastern WI and I have a medium colored green growth covering much the trunks of my maple (October Glories and a Schwedler)trees. It has been there now a couple of years and I was not concerned about it until now. It appears that the bark of one of the larger (Schwedler) maples (about 15 years old) is starting to peal off. The green growth looks like it would be a fungus or lichen of some sort. I have tried to look up some information on line about it, but I am unable to find anything that sounds like what I have. The same green growth is also on the trunk of a now dead (young) Bradford Pear tree. And I now wonder if this is what killed it?
Can you help me identify this and tell me if you think it is indeed a problem?
Thanks!

Answer
Sounds like one of the 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 did not kill the Bradford pear.
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.