Answer: Algae, lichen, and moss grow profusely on trunks, limbs and twigs of many trees and shrubs due to the cool, cloudy, wet weather in Western Washington. These are simple plants that manufacture their own food, so other than being unattractive, they do their hosts no harm. If you use lime-sulfur to prevent disease on your fruit trees, it should kill the algae as well. Spray during the dormant season (winter). The algae will slough off with subsequent rains. Lime-sulfur is safe to use on azaleas, but at different concentrations. Read and apply according to label directions, making sure that the plants you want to use it on are listed on the label. There's really no way to prevent the growth of algae, lichen and moss, but you can control it with applications of lime-sulfur.
Q&A Library Searching Tips