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While many growths on trees are not an indicator of a problem, they sometimes indicate a serious issue that, if left untreated, can cause a lot of damage and/or injury. When in doubt, always call an arborist to correctly diagnose a foreign growth on a tree. Read through the list below to learn about some of the common types of growths that are found by Mead Tree and Turf Care arborists.

by Tina Graver, Certified Arborist


One of the most common questions we get as arborists is about lichen growing on the trunks of trees.  It is generally light/pale green in color. Lichens are a symbiotic organism made up of an algae and a moss. They are completely harmless to the tree they are growing on. Most common in a more humid landscape, lichens are slow growing and long lived. Lichens are also a food source for deer when other food sources are scarce.


Moss can also be found growing over the root system or on the main trunk of some trees. This is predominantly in moist, cool and shaded areas. Moss is not an indicator of something wrong with the tree, nor does it adversely affect the tree’s health.  At most, moss can indicate a very wet area which may or may not be suitable for a given tree species.

Shelf Fungus

Generally, a shelf fungus is an indicator of a problem, especially if noticed on older trees. If you notice a shelf-type fungus on any of your trees, you should have a certified arborist look at your tree right away.  One aggressive type of fungus known as ganoderma root rot can overwhelm a trees structural integrity very quickly. There are no treatments to stop or suppress this disease. Ganoderma is a root rot fungus that can cause very large trees to fail at the base. This is the same disease that eventually caused the historic Wye Oak to fail.


Yellow mushrooms

The other aggressive type of mushroom arborists look for is armillaria. This root-rot fungus is very similar to ganoderma root rot in that it can’t be treated. Armillaria is identified by its orange mushrooms and black, shoe-string like, rhizomorphes that penetrate the bark of a tree. Mead Tree and Turf Care recommends having any suspicious mushroom looked at by a certified arborist.

Small white mushrooms along stems

Most mushrooms are white in color, which makes their identification difficult. The first clue arborists look for is whether or not the mushroom is growing on a live limb or not. If the limb is dead, then the mushrooms are usually secondary decay, meaning they started growing after the limb died. If the limb is alive, they could indicate a saprophytic fungus that is growing on the live part of the tree. This is usually a detrimental disease that can cause the tree to fall apart, limb by limb. Finally, it could be a wood decay fungus in its early stage of growth. Again, mushrooms like this should be diagnosed by a certified arborist.

Wet spots

Wet spots may be caused by many things. Some are called cankers and generally indicate a tree under stress. While there is no direct treatment for the canker, a certified arborist can help a home owner address and mitigate the stress factors. Wet spots could also be caused by wood-boring insects. Early intervention with protective measures could help preserve a tree that is being attacked by insects. Like cankers, borers are attracted to trees under stress. In addition to insecticides, steps should also be taken to help minimize the stress factors affecting the tree.


If you notice swollen limbs or small bumps on leaves, this may be what is known as a gall. Galls are produced by the plant or tree as a defensive measure against a pest or disease. Galls are normally benign and more of an aesthetic nuisance than anything. Selective pruning or insecticides may help.