Why is Mold Growing on My Tree Trunk?

Have you recently noticed a greenish-white or orange-colored film developing on the outside of your tree’s bark? Is so, you may assume it is mold, but really, it is a harmless fungi known as tree lichens. Continue reading to learn more about tree lichens, including its causes, treatments, prevention, and more.

Noblesville Tree Service 317-537-9770
Noblesville Tree Service 317-537-9770

Tree Lichen Fungus

Tree lichens are actually two living organisms, fungus and algae, which both share in a mutually-beneficial relationship known as symbiosis. The fungus collects and retains moisture, which algae needs to thrive, while the algae uses photosynthesis (converting the sun’s energy into food) to make food for the fungus to feed on. This symbiotic relationship does not negatively affect trees in a physical sense. Tree lichens contain rhizines, which are similar to a root system, but they do not reach far enough into the ground to affect the tree’s root system in any way.

Getting Rid of Tree Lichens

Although tree lichens will not damage or kill a tree, many homeowners complain that it makes their landscaping trees look bad. Fortunately, there are some simple and effective methods for removing tree lichens from trees, safely. Here are some recommended methods to try on your own landscaping trees:

❧ Scraping

You can gently scrape tree lichens off of the bark of trees using a mild soapy solution and a soft bristled brush. Combine a mild dish soap with some clean, warm water, and then delicately apply the solution to the affected areas using your soft scrubbing brush. Be very careful with the amount of pressure you use to scrape away the film; scraping too hard can harm the tree and leave it susceptible to pest infestations and disease.

❧ Copper Spraying

You can also apply a copper-sulfate solution to the bark of your trees during warm seasons to kill the tree lichens and prevent them from growing back. It will not work in cold weather. Also, keep in mind that a copper-sulfate application will only take care of the fungus, as it does not target the algae side of the lichen outbreak. For this reason, you may need to follow up a copper-sulfate application with a secondary treatment of soap solution.

❧ Lime Sulfur

Another common treatment used to manage tree lichens is lime sulfur applications. Lime sulfur can be purchased in the horticulture section of any local home improvement or garden store in powder or liquid form. Typically, you can acquire a quality product under $20 or so. Just be careful not to contaminate the tree roots or leaves with this product, as it can cause severe damage to the tree.

❧ Environmental Modification

For those who like an organic, Eco-friendly approach, you can attempt some environmental modifications to prevent tree lichens from developing on your trees. You see, tree lichens grow best in partly sunny, moist environments. So if you change these conditions around your trees by thinning out tree canopies, trimming leaves, or removing sprinkler systems, you can abate tree lichen development for seasons to come.

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Noblesville Tree Service 317-537-9770
Noblesville Tree Service 317-537-9770