You may have noticed a green, moldy growth growing on your mature maple trees. The green patches are most likely caused by lichens, which often find a home on older trees. A lichen is made up of an algae and a fungus, which symbiotically live together and create a new body, known as lichen thallus. This can cover most of the tree trunk, creating a greenish coating. When lichens decay, they nourish new growths, such as moss, creating more green on your trees. Treat the trees to remove the lichens and reveal the trees' natural, brown bark once again.
Turn on your sprinklers, if you have any, and observe where the water hits the tree. If the water hits the lichens, it is helping them survive. Adjust the sprinklers so they do not hit the lichen-affected areas.
Prune out dead or weak branches to open the canopy and allow more air circulation through the branches. This may deter lichen growth. Dispose of the branches in case lichens are present.
Spray the lichens with a ready-to-use, copper soap fungicide, following the manufacturer's instructions. Scrub the bark of the tree with a soft-bristle brush, being careful not to scrub the bark off. This helps to remove lichens and kill the fungus.
Treat the trunk of the tree with a dormant lime-sulfur spray around January. The lime sulfur kills the fungus and creates protective film to prevent the entry of fungus into the tree. Follow the manufacturer's instructions when using the product.
Spray the tree with a copper-sulfate fungicide when the temperature is above 40 degrees F, usually in late spring or early fall. The copper-sulfate kills the fungus and prevents lichen growth. Follow the manufacturer's instructions as to how and how often you need to treat the tree.
Monitor the tree for future lichen infestations. Repeat the treatment process if needed.