What Is the Gray Mold Like Substance Growing on the Side of My Tree?

— Written By and last updated by Patricia Burch

Lichens are a common site on branches of trees and shrubs. Seeing lichens can be an unusual site because it looks like a strange organism is taking over the plant. It is often thought that lichens are a fungus or disease that is damaging the plant but in reality that is not the case.

Lichens are unique organisms. It is a fungus and algae combined to live together. Although lichens really do not look like a fungus or algae both work together so that lichens can survive. The algae use photosynthesis to produce food while the fungus supplies water and structure. This combination allows for lichen to be very adaptable to extreme environmental conditions.

 Lichens can be found on a wide range of surfaces including limbs, branches, stumps, rocks, fence post, and even on the soil. Lichens firmly attach themselves to these hard surfaces. This gives the impression that lichens are sucking the life out of a plant when really they are living on their own and producing their own food but use the branches as a place to attach itself to.

 Lichens prefer to locate themselves on surfaces exposed to sunlight. When lichens are seen on branches of a tree or shrub the branch usually has little foliage giving the appearance that the lichens are causing the plant to decline in health. Lichens do not cause plant damage but instead are a sign that the plant itself is declining in health due to some other cause like environmental stress, poor management, or being planted in the wrong location. When the plant is stressed or unhealthy, typically a decrease in foliage occurs allowing branches to be more exposed to sunlight, thus providing a great location for lichens to call home.

Keeping plants in good health is the best way to reduce the amount of lichens found on plants. A heavy infestation of lichens is a sign that the plant is currently in poor health. Extremely high infestation of lichens maybe a sign that the plant needs to be replaced. Keeping a plant healthy by proper watering, fertilizing, location, and care will encourage a thick leaf canopy and reduce the amount of lichens. For limbs with a lot of lichens, light pruning can remove some of the lichens and stimulate new growth, which will help shade out the rest.

Keep in mind that lichens is a sign of poor plant health. However, do not be alarmed if you see a few lichens here and there. A few lichens here and there on a plant are suitable. So when you see lichens on shrubs or trees remember that the lichens are not causing the problem, you may want to consider the plant’s health and how to improve it.

Reminder:  If you would like to learn more about Horticultural related topics, then join the “Sampson County Friends of Horticulture”. This program offers monthly “How To” Horticultural Seminars. Please call (910) 592-7161 for more information. Please call the Sampson County Cooperative Extension Center at (910) 592-7161 with your horticultural questions and to register for any upcoming events. Be sure to check out the Ask An Expert Widget at sampson.ces.ncsu.edu for any questions you may have.