What To Do About Mold on Tree Bark

When observing the trees on your property, do you notice little splotches of bluish-green color on them? It doesn’t look like moss, so what is it—mold on tree bark, maybe? And while some growths won’t harm your trees, others, like mold, might. So how do you manage what might or might not be mold on tree bark?

First, there is a way to distinguish between the various forms of organic life that can adhere and propagate on the bark of trees. And in terms of identifying the growth of mold on tree bark, there are databases replete with photos and symptoms of different ailments. Listed below are a handful of common organisms that grow on tree bark and what you can do about them.


Generally speaking, the “mold” to which many refer is usually lichen. That said, mold can, in fact, grow on tree bark. When certain insects arrive on a plant or tree, they excrete sugary substances, and then mold spores attach and grow on the sweet excretions. For example, aphids leave behind honeydew. Usually, the insects leave these excretions on a tree’s leaves, but sometimes, the substance drips down onto other parts of the tree, including the bark, where mold can further spread.


Lichen is an organic form of life that grows on the trunks of sick, diseased, and unhealthy trees. It does resemble mold, but it is comprised of composite organisms, fungi, and algae. The presence of lichen on a tree does not signify decay or degradation, as the root-like structures of lichen act more as an anchor and don’t break through the bark into the tree. It is a self-sufficient organism that doesn’t take anything from the tree, not even nutrients. Lichen produces its own food.

As an unwell tree starts to further deteriorate and die, the leaves wilt and fall, exposing the lichen to more sunlight, helping them to grow. As they increase in size, the presence of lichen suggests that it is the culprit in the downfall of the tree.

A tree that is unwell may have lichen and additional—and unrelated—organisms attached to and growing on different parts of the tree. The best way to care for the tree is to get right to pruning and removing the sick branches and dead tissue to support the health of the rest of the tree.


Moss is a rootless plant that can grow and thrive on trees—among other surfaces—and survives off nutrients and water that collects on the tree (not from the tree itself). It can also grow and thrive in really moist regions where the moss can simply absorb some of the moisture from the air. Occasionally, it can even grow in traditionally drier places, so long as there is a consistent water source, such as condensation or groundwater seepage, the presence of water can sustain the moss.


Mildew generally appears as a powdery growth on both the leaves and the bark of trees. The white growth is what millions of microscopic fungal spores look like when they collect on a surface. There are some trees that are more predisposed to having mildew issues, and they can include linden, chokecherry, and crabapple trees.

Black Mold

This type of mold, also called sooty mold, looks worse than it actually is. The mold grows on leaves and prevents them from taking in enough sunlight, which in turn, can stunt the growth of the tree or bush. This brackish, black film can be found on the surface of the leaves and usually indicates that insects are responsible for the presence of the disease.

In order to prevent insects from returning and further undermining the health of the plant or tree, neem oil can be used as a natural repellent. Natural repellents are easier on the host organism (read: tree) and can be equally as effective against pests and invasive organism growth.

How to Treat and Control the Growth of Organisms on Tree Bark

While moss and lichen really don’t pose any risks to the bark of trees, they can be a bit unsightly. If any pruning or dead branch removal is necessary, then it’s a good idea to follow through with that, but as long as some form of water or moisture is present, lichen will continue to grow.

When it comes to other organisms on the surfaces of the tree, there are different treatments needed. A natural approach to protecting the foliage of the trees is using a naturally occurring repellent, such as neem oil, as mentioned above. There are other natural solutions for issues like mildew too, but if you’re looking for a quick way to remove powdery mildew, you can use a sulfur mixture (at 2 to 4 pounds per 100 gallons). This chemical solution should not be used in the heat, as the sun can damage the leaves that were treated with sulfur.

When you start to look for other solutions to treating your trees, be aware that some solutions will discuss the use of bleach or other heavier-duty chemicals. These can not only harm people, but the plant life and shrubs around the trunk of the tree, including the tree itself. Before opting for the chemical and heavy-handed approach, look at more gentle alternatives to see if they can provide a solution to the mold or mildew growth on your trees.

Hiring the Professionals

As with any tree services, only trained, certified professionals should be consulted for tree pruning, removal, stump grinding, and disease diagnostics. Mr. Tree is your local team of professional arborists and tree experts, and we’re here for any consultation needs for all residential, commercial, or industrial property needs.

What sets us apart from other comprehensive tree service companies is that we have decades of combined knowledge, stay consistent in our training and review certifications, and have developed a strong track record with satisfied clients.

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