Question
There is this light light green, almost silver scaley stuff covering the bark on several of our trees. It is so thick it seams to be smothering them. It is also on all of my Lilac bushes. We live out in the country in Texas so no real experts to ask. Only samll town feed stores. Please help....

Answer
These are called lichens and are not a problem.
Lichens are an example of a symbiotic relationship between algae and certain fungi. They are capable of producing their own food. The algae associated with the fungus is a green or blue-green alga. There are three forms of lichens based on growth patterns. Crustose are species that are closely pressed against the surface of the limb or trunk of dead or live trees. Foliose forms are leaf like or prostrate but are also tightly attached to the tree. Fruticose forms are bush like, erect or hanging. Although lichens are found in most areas of Texas, they are most noticeable in areas that have extended periods of high humidity.

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.

Copper containing fungicides are suggested as possible controls for lichens. Applications of Kocide DF  have been observed to control lichens for a short period of time. Presently, no pesticides are registered for the control of lichens commonly found on the twigs and branches of shrubs and trees.  Kocide 101 77W (1 level tablespoon per gallon) and Kocide DF (?level tablespoon per gallon), applied at the rate of 1 pound of product per 100 gallons of spray volume, will control the lichen