Question
Hi, we have a really big maple tree. we noticed today that it has some strange white spots on some of the branches.( the bark itself is white) on the other parts there is  a lot of other circles that are very pale green and it looks like they are turning into moss. do you have any suggestions for us? thank you,Kim

Answer
IF the bark is not loose this is not a disease. I would guess it is a lichen.

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  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.

lichens are combinations of green algae and fungal tissue. Each lichen specie is one alga species plus one fungus. The alga, a microscopic green plant, makes the food for the duo, while the fungus, a non-green plant, gives the pair support and soaks up moisture.

This cooperative arrangement benefits both creatures and the surrounding system, but raises a frequently asked question...Are lichens harmful to your trees?


No. Those grayish-green patches, usually one to three inches in diameter, are not feeding on your trees. Since lichens are able to make their own food with moisture and sunlight, they have no need to parasitize other plants. Lichens grow on the surface of your tree, and do not penetrate any tissue. Instead, they make use of the trunk or branches for support. They do not cause plant diseases either, with one exception: in certain wet, tropical areas, lichens have grown in such thick layers over trees that their shade alone has caused leaves to die.

They cause no real health issue to the tree. As long as the foliage is green and healthy looking there is no problem.