Lichens are often found growing on rocks, window-panes and plants. They are harmless but could indicate that something is wrong with a plant or tree.
Lichens usually don’t grow on young, healthy, actively growing trees and shrubs. As long as an object is growing (or moving), lichens can’t take hold. On the other hand, stressed trees and shrubs grow very slowly and often have lichens growing on them.
Lichens are not pathogens, meaning they don’t cause disease in plants. They use the plants as a surface to grow on. When a tree or shrub begins to decline due to some sort of environmental stress or other disorder, its leaf canopy will thin and allow sunlight to enter and support lichen growth. If overall plant health is improved, a dense, vibrant leaf canopy should inhibit any sunlight available for lichen growth.
Lichens are often found growing on trees planted in the lawn. The two most common causes for stress to trees and shrubs is injury to the plant from trimmers and trimmers, and poorly drained soils. Other reasons include herbicide damage, poor plant quality and planting technique, and forgetting to remove plant ties and plastic name tags that can girdle branches.
If you see lichens growing on trees and shrubs in the landscape, this is a clue that something is causing your plants to grow slowly and decline in health. This could be a combination of factors like plant competition, drought stress, root stress, over watering, soil compaction, poor nutrition or improper soil pH.
If you remove what’s stressing your trees or shrubs (correct the pH, improve drainage, apply fertilizer improvement of air movement around the plants), the lichens will go away and the plant’s overall health will improve. A fungicide containing copper can also be applied to aid in control.