Lichens often take the brunt of angry homeowners wondering what causes frilly blue-green growths on a tree trunk. These growths do not cause harm to trees, but are a sign of poor tree health.
Regional Extension Agent Beau Brodbeck said blaming lichens for hurting trees is nothing new.
“Most people blame the frilly blue-green growths on a tree trunk for health problems,” Brodbeck said. “The problem with your shrubs or trees may be poor soil fertility, root disease or circling and girdling roots. These problems are often below ground and difficult to immediately identify.”
Lichens are composed of a fungus and a green or blue-green alga growing together. The fungus absorbs water and minerals from both the air and the structure to which it is attached. The alga uses photosynthesis to convert these materials into carbohydrates and vitamins. Unfortunately for homeowners, lichens are hearty and can grow in some of the world’s harshest conditions, including deserts and arctic tundras.
There are three distinct varieties of lichens in the southern part of the United States. One grows flat, looking like a white, gray or blue-green splotch with little raised definition. The second variety forms leaf-like folds that are frilly and the third develops branch-like structures, which are often long and hair or coral-like.
While most lichens occurring on trees are a gray-green in color, there are others in a variety of colors ranging from dark brown to yellows and even bright oranges. In South Alabama, it is not uncommon to see orange and almost salmon-colored lichens on live oaks.
Brodbeck said lichens on trees and shrubs occur regularly on branches and trunks exposed to full sun. As a result, trees with thinning leaves or missing branches will have more lichens on exposed inner branches.
“Here is where many misconceptions about lichens are born,” he said. “We see declining health in trees. Then we assume it’s the lichens that are causing tree decline and seek out costly chemical controls that are not addressing the tree’s problem.”
Brodbeck has several recommendations for short-term care:
- Look for circling or girdling roots. Cut them with a sharp saw.
- Test the soil. Tests are available at your local extension office.
- Look for fruiting fungus. If present, contact a Certified Arborist.
Long-term care options include:
- Mulch around trees and shrubs. (Apply 2-3 inches at drip line, not the trunk base.)
- Water trees during periods of extreme drought.
- Remove trees and shrubs that do not respond to recommended treatments.
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