Lichen is a simple plant form that can grow on any flat surface as long as there is light. Lichen signals good air conditions, as it is intolerant of pollution. It is a fascinating creature that is made up of a fungus and an algae that are symbiotic. The majority of lichen prefers temperate to arctic conditions, although there are some tropical forms. Sunshine and water are the key growth components for lichen, but it gets its nutrients and moisture from the air. Lichen causes no damage when growing on trees. They are using the trees only as perches. Lichen can be removed to improve the ornamental value of the tree.
Remove the lichen manually by wetting it completely and scrubbing it off with a scrub brush. This may take several attempts. The problem with this method is it can abrade the bark of the tree and possibly cause the introduction of pathogens.
Cover large sections of lichen with shade cloth. Tie it on the branches using old nylons, as they are flexible and make excellent plant ties. Covering the lichen removes one of its main needs in the form of sun.
Plant taller trees and shrubs that will give more shade to the area. Removing the bright sunlight will cause the lichen to starve and die.
Spray copper sulphate on the limbs to kill the lichen. Copper sulphate will kill the fungus part of the organism. Apply the copper sulphate in spring through early fall when temperatures are warm. Follow the label instructions for application details.
Lower the risers on your sprinkler system. If the sprinkler heads are set too high, the lichen may be unintentionally getting water that promotes growth.