Plant Pathology Infobytes
December 21, 1998
Lichens - No Danger to Landscape Plants
Lichens are among the most fascinating of Mother Nature's creatures. They are found in a variety of sizes, shapes, colors, and habitats. However, when these creatures invade landscape trees and shrubbery, homeowners frequently become concerned about possible damage to landscape plants.
If you remember your high school biology, you probably recall that a lichen is actually made up of two components -- a fungus and an algae living in association with one another. However, the appearance is that of a single plant.
Lichens manufacture their own food and grow on soil, on rocks, and trunks and branches of trees and shrubs. They occur in several forms such as crusty gray, green, yellow, or white growths. Some are leaf-like, others resemble a tuft of horse hair hanging from branches.
Lichens are amazing creatures for other reasons as well. They frequently serve as a source of food for snails, mites, and insects. In subarctic regions, lichens are a food source for reindeer and caribou. In hard times, lichens have served as a source of food for man, such as when Washington's troops at Valley Forge used lichens as a soup thickener. Today, lichens still serve as a source of natural dyes used wool and other clothing materials.
In the home landscape, lichens most often appear on plants that for some reason are in a poor or declining condition. Why lichens tend to "pick-out" weak plants as preferred colonization sites is not entirely understood. But for whatever reason, such plants often support profuse lichen growth, and it's easy to understand why home landscapers think the lichens are responsible for poor plant growth.
It's important to realize that lichens don't cause the plant to grow poorly, but they may indicate that something is wrong. So when your azalea, camellias, plum or apple trees, or other landscape plants are affected by these oddities of the plant kingdom, remember it's not the lichens that are the problem. It could be an entirely normal occurrence, since lichens also occur on healthy plants, or a signal that your plant has something else affecting it.
If you need assistance in identifying problems in the home landscape, give us a call at your county Extension office.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.