It's not killing your trees

Circumstantial Evidence

Though it may appear that lichen is damaging garden trees and shrubs, nothing could be further from the truth, as this plant partnership merely takes advantage of the host plant's misfortune.

Being the horticulture Extension agent for the county, I frequently help clients with calls and concerns about their plants, lawns and gardens. I typically Play many roles – plant doctor, detective and psychic – to solve problems. One call that I occasionally receive in the winter concerns a “fungus” growing on certain plants.

Folks usually declare, “This stuff is killing my plants!”

Once people begin to describe what they are seeing – some gray, paperlike stuff – I immediately recognize what they are describing. I calmly respond by saying, “It’s not a disease, and no, it is not hurting or killing your plants. It’s just lichen.”

Lichens are often blamed for the decline and death of numerous shrubs and trees in Alabama landscapes and gardens. That’s not surprising because these unusual plantlike organisms are commonly seen on the exposed limbs and trunks of declining or deceased plants. They can be found on mature azaleas, dogwoods, pecans and neglected and old fruit trees. But then again, you will see lichen commonly growing on the sides of mature tree trunks, exposed rocks, old wooden fence posts or aged birdhouses.

Actually, lichens rarely have anything to do with poor growth or death of ornamental plants or fruit trees. One theory is that their appearance often indicates environmental stress or poor management.

Lichens colonize a wide range of exposed surfaces of limbs, stumps, soil, rocks, stone, metal, glass, plastic, cloth and other living and nonliving objects. They are most numerous on limbs and trunks of large mature trees and shrubs in full sun, particularly those plants with badly thinned canopies. Lichens only require undisturbed surfaces, time and clean air. They are considered opportunists and can grow anywhere it is sunny. Exposed limbs on damaged plants simply give lichens access to the sun they need for growth with little competition. Lichens firmly attach to these hard surfaces; however, research has shown that lichens do not damage plants or rob the bark of moisture.

These often inconspicuous, hardy and adaptive plants are composed of a fungus and a green or blue-green alga. This union or symbiosis produces a long-lived organism that does not look like either the fungal or algal partners. Both partners contribute to the growth of the lichen. The alga uses photosynthesis, like other plants, to produce food while the fungus supplies water and essential minerals and produces a structure that protects the alga from extreme environmental conditions. Together, they thrive in some of the harshest environments on Earth, in places where few other plants and neither partner could survive alone.

In 2016, scientists at Purdue University uncovered a third partner – yeast. It is believed that yeast enables the lichen to produce acid that helps defend it against invasion from other microbes.