Question
I am emailing you for a friend of mine. Her father has several fruit trees and they have gotten some type of fungus on them. The fungus is almost grey in color and it looks like moss. It is covering most of the trees. He said someone told him to get dish detergent and put it in a spray bottle and spray the fungus with that. He wants to get another opinion because he does not want to harm the trees. I would appreciate your opinion on this. Any suggestions would be welcomed. Thank You, April

Answer
These are called Lichens. The soap will not effect them. The main problem is more than likely the declining health of the trees. I would recommend that the trees be fertilized and the dead branches or branches that are crossing be pruned off.
Nature is full of mysteries and there is a fascinating one just outside in your landscape. We don't have to look very far to find one of these marvels of creation, the lichen, thriving in our warm, humid, Mississippi climate. At first glance, the papery or fuzzy, white, gray or green growth might lead us to believe that lichen are just another parasite, working to destroy our landscape trees and ornamentals. Although lichen are often found associated with plants that are dead, dying or declining, we must remember that this is only circumstantial evidence, and the lichen is innocent until proven guilty.

Remember way back (for some of us) in junior high school science class when we first learned the meaning of symbiosis? A symbiotic relationship is one in which two organisms live in close relationship with one another to the benefit of each. Such is the case of the lichen. What appears to be one organism are actually two, an algae and a fungus living together that have formed one body. The algae, a green plant, can make its own food, and in this case, shares with the fungus. The fungus, on the other hand supplies the structure, or thallus, within which the algae lives. Lichen can be found attached to healthy plants or those in dead or dying condition. Although sometimes unsightly, they are not parasitic and do not contribute to the poor quality of a plant.

Believe it or not, lichen is actually beneficial to humans for several reasons. First, they are sensitive to air pollution and are commonly used by researchers to determine the air quality of a region. If lichen thrives in your neighborhood, it's a good indicator of quality air. Drug companies use lichen substances to make antibiotics. Some lichens make nitrogen in the air more available to other plants. People eat some lichens but remember a few of them are poisonous! Lichen can also be used to make dye for coloring wool.

It is usually not necessary to treat plants to control lichen. The best practice is to keep landscape plants healthy and growing vigorously. However, for trees and shrubs that lose their leaves in winter (including fruit and nut), tribasic copper sulfate may be used at the rate of 4 teaspoonfuls per gallon of water to remove unwanted lichens. Add a spreader sticker to the spray mix and avoid contact with evergreen plants.

Here is a web link to pruning fruit trees. You may want to contact the local office of the Agriculture Extension and ask one of their experts to come take a look.  

http://ucce.ucdavis.edu/files/filelibrary/2002/3363.pdf

http://extension.unh.edu/Pubs/HGPubs/fertfrt.pdf