Many things can negatively affect your trees, including tree mold and mildew. It can be concerning if you've seen green stuff growing on trees, black algae on trees or any other type of growth. Luckily, not all tree mold and mildew are harmful, and you can control those that are detrimental. There are many types of tree molds and tree mildews, and once you identify which one is your problem, you can identify and treat it.
Is It Lichen?
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If you see something growing on your tree, particularly greenish fungus on trees or green stuff growing on trees, it can cause concern. After all, a dead tree can fall and damage the structures around it, including your home. If what you're observing appears to be a green fungus on tree bark, the chances are good that it is a species of lichen or perhaps even moss. Moss and lichen growth is almost always harmless for the tree and can even be beneficial in some cases.
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Moss is easy to identify by its texture. Lichen sometimes looks like moss, as it is usually green or brownish-green. It is typically flat or leafy and can even be a bit crusty if you try to pick a small piece of it off the tree. You may notice a sudden growth of lichen in the late spring after it has been wet and then a reduction in the late summer when it's hotter and drier. Experts recommend letting lichen grow; removing it may cause unnecessary damage to the tree bark since it is harmless.
Tree Mold and Mildew
While lichen is harmless, other growths are not. You may notice white fungus on trees, mainly white fungus on tree bark that looks and feels powdery. While a tree trunk can usually withstand this growth, it will likely wilt and die if it gets on the leaves.
Some appearance of powdery mildew is normal, especially if conditions have been good for it. Rainy and humid conditions with temperatures between 60 and 80 degrees Fahrenheit are ideal for this mildew. Keep records and even take pictures over a couple of weeks to determine whether you can let it run its course or if you need to take action to get rid of it.
If you see black algae on trees, it's likely a mild sooty mold fungus. Like the powdery mildew, this type of tree mold isn't harmful unless it proliferates and begins to attack the leaves. If it does, you'll need to take steps to prevent the tree from dying.
How to Treat Mold and Mildew on Trees
Basic tree maintenance can go a long way in preventing tree mold and mildew growth. Every year, trim away excessive growth, particularly underbrush and dead branches. Powdery mold in particular needs damp, shady conditions to grow. Don't compost any foliage that has a growth on it.
Before using any chemicals, try spraying the trees with water from the garden hose. Use enough water pressure to break up the mold and mildew without damaging the trees. Sometimes, that's sufficient to remove enough of the growth so that it doesn't threaten the trees anymore.
One of the most effective treatments for tree mold and mildew is neem oil. Best of all, it's a natural pesticide found in the seeds of neem trees. You can buy this oil at garden centers and hardware stores. Follow the manufacturer's instructions for using it. While it is natural, it can irritate human skin and eyes, so wear protective gear when using it.