Question
purchased a home with a beautiful tree filled yard, but they all seem to have a blue grey mold or fungus growing on the trunks and branches, lots of it. we live in the midwest, so it's on a variety of pines, two apples, two flowering crabs and two pear trees. Seems to be affecting the fruit trees. The pear trees are dying it seems, one has barely any leaves and no fruit, the other also has spots on the leaves and the fruit is only at the top and falls off and dies before ripening. any ideas? any advice would be wonderful. thanks for the help

Answer
It sounds like you are describing lichens.  Lichens are a unique because they are actually two organisms living together, a fungus and a green alga.  They are very diverse and come in many different colors and shapes.  

Lichens do not damage trees, they merely use them for support.  If you notice the lichens on plants that are ailing, it is simply a coincidence.  Lichens need light for growth, so it makes sense that they would be high up on dead or dying limbs where light is readily available.  They do not injure plant tissues and only grow on the surface.  

It is very hard to grow fruit trees in the midwest, so that is probably why you notice them more commonly on these trees.  The canopies of the trees are often more open and the lichens receive more light.

For more information about lichens, this link will take you to a fact sheet from Ohio State University.  http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3312_09.pdf

Good luck with your trees.
--Jen