By Chris Hicks, County Director – UT Extension Smith County
“What’s This Fungus Killing My Tree?”
It seems this has been a record-setting year for calls about trees. I’m not sure if that is because more folks were home due to Covid-19 during the spring and early summer and therefore had more time to look at their trees, or if trees really have suffered more than usual during 2020.
I can tell you that the trees I have looked at this summer have had a variety of issues, from insect damage such as Pine Sawfly and Imported Willow Leaf Beetle, to diseases like bacterial spot and Seiridium canker, to environmental damage caused by a combination of a drought last fall and a late freeze this spring. We’ve even seen some instances where trees were planted improperly years ago and are just now showing the effects.
One common question we get is about a fungus on trees. While there are some fungi that can damage trees and other plants, one of the most common we see is a harmless combination of a fungus and an alga called lichens (pronounced likens).
Lichens do not have roots, stems, or leaves, so they absorb most of their nutrients from rainfall. Because of this, they can grow in places that are impossible for other plants, such as rocks, bridges, railroad tracks, roofs, and stone monuments. Just as these lichens are not killing the bridge or rock wall they hang out on, neither are they killing the apple, oak, or willow tree in your backyard.
Lichens are not parasitic and do not consume any of the plant or poison it. They merely live attached to the surface. Some remain virtually flat on the surface, while others have curly leaf-like structures.
While the lichens themselves do not harm trees, they are sometimes an indication of a problem. Trees that are thinning due to disease, insect, or environmental damage will allow more light into the interior limbs which can increase lichen growth. The appearance of lichens as the tree declines leads people to think the lichens are at fault. In reality, they are a symptom of an existing problem, not the cause.
Lichens can be unsightly even if they are not harmful. If you want to get rid of lichen growth, you can do so by gently brushing it with a scrubbing brush, being careful not to damage the bark of the tree. Improving overall tree health through proper watering and mulching can also increase foliage which will take away the sunlight lichens need to survive.
While there are plenty of pests that can cause trees to die, lichens are not one of them. For more information on growing healthy trees in the landscape, visit smith.tennessee.edu or give us a call at the University of Tennessee Extension office at 615-735-2900.
