ALGAE ON LEAVES
Found on evergreen trees a green, powdery deposit on leaves can make them dull and unsightly. These are caused by algae which are harmless to the plant but they do cut out precious light to the leaf surface. Not to be confused with sooty mould which a pest-caused problem, a sap sucking pest which can be washed away with a soapy solution.
Caused by damp shady conditions, leaves of deciduous trees and shrubs tend not to be affected as they drop each year before the wet winter months and are replaced with fresh in the spring. Prevent by spacing trees well apart to ensure air circulation and more light.