Azaleas are normally a plant with a dense, leafy canopy. But as azaleas decline in health, a mossy growth called lichen might start to grow on the trunk and branches. If you take a walk in the woods, you may see lichen growing on the trunk of trees or on the side of a mossy rock. Lichens are not harmful to plants, but can be found on neglected or diseased plants because of the increased sunlight that these plants are allowing on their trunks. Increasing the health of your plants will get rid of lichen long-term. But there are short term solutions.
Wait until after a rain to remove lichens. Rain typically loosens lichens, which makes them easy to remove.
Buff lichen away with a gentle nail brush by rubbing the lichen with the brush in a circular motion until it is gone. As you rub the lichen, be careful not to damage the bark of your azalea plant.
Spray the lichen with an organic fungicide, such as one containing sulfur or copper. This will typically kill lichens without harming plants.