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The causes and remedies of lichens
Ingram Sam
Effingham County Extension Agent Sam Ingram

Something growing on many of our landscape plants is causing concern for homeowners. It may resemble a small patch of green hair or other specimens may look similar to grey pieces of paper. The assumed pests are actually fungi called lichens and actually do not cause damage to the plants, but are a sign that the plant may be declining or under stress.

Lichens are found on rocks, tortoise shells, window panes and plants. As plants are stressed and begin to decline, the reduced canopy allows sunlight to enter and support photosynthesis for the lichen. The most important thing to understand is that the presence of lichens is an indicator of poor plant health but it is never the cause.

Lichens are harmless to plants and, if overall plant health is improved, the vibrant canopy should inhibit any sunlight available for lichen photosynthesis.

If lichens are not the cause of poor plant health, then what is? Two underlying factors I discovered while investigating these problems are 1) age/plant stress and 2) soil fertility issues. As a tree ages it naturally declines. Sunlight penetration into a declining canopy allows lichens to grow. Sometimes, trees such as dogwoods are planted out of place. A tree that likes shade and is planted in full sun consequently grows in a stressful environment.

The other factor in plant decline is soil fertility. Recently, I came across a serious case of lichens I had not observed before. I noticed the lichens only covered a few of the trees at the site. We took a soil sample on the declining trees and found the pH to be over 7. This is critical since plants cannot take up nutrients when the soil pH is too high or low.

If you notice a younger tree with lichens, and all other trees seem to be OK, take a soil sample. If the pH is too low, it can be corrected and fertilized. This will encourage a more vigorous canopy which eliminates sunlight that lichens need. If the tree or plant is very old, it may have a natural decline. In this case, there is not much that can be done.

For additional questions, contact Effingham County Extension Agent Sam Ingram at 754-8040 or singram@uga.edu.