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​Should I Worry About Fungus on My Tree Bark?

The sight of ​fungus on tree bark is not especially pleasing. Imagine taking great care of your trees, only to be greeted by scabs on the bark. Unfortunately, tree fungus is one of the most common ailments that affect plants, and if left untreated, it can result in the death of your trees.

But does that mean the alarm bells must go off as soon as you spot any fungal growth on your tree bark? Let’s break it down for the uninitiated and find out when you need a professional arborist like Mr. Tree to intervene.

Are All Fungi Harmful to Your Trees?

While the appearance of shelf mushrooms or lichens on your tree bark is relatively safe fungal growth, there are deadlier versions that are fatal for your tree. These include Rhizosphaera needle cast, cedar apple rust, Botryosphaeria obtusa, and powdery mildew.

Spotting fungi on your tree should be a cause for concern, as it can adversely impact the structural integrity of your tree. It can also attack the leaves, preventing the tree from completing vital processes, such as photosynthesis. Fungal spores cause calluses or large rot wounds on your tree bark. If left unchecked, it can also speed the rotting of your tree.

How Will You Know Fungus Has Attacked the Tree Bark?

Look for black-, brown-, or red-colored lesions—these may penetrate the bark and cause canker disease. Also, check if the bark is falling off from the tree and decomposing at the base.

What Are the Common Fungal Diseases That Can Affect the Bark?

Here are some of the more common tree bark diseases you should be aware of:

Dutch Elm Disease

This is an invasive fungal infection that attacks various species of elm trees. It’s spread by elm bark beetles carrying fungal spores. The beetles dig directly into the bark to lay their eggs. When the larvae hatch, they bore deeper into the tree and eat the healthy tree sap while damaging the vascular system of the tree. In trying to block the spread of the fungus, the tree ends up blocking vital nutrition from circulating. Gradually, the tree starts wilting and ultimately dies within one to three years. One of the first noticeable signs of this fungal disease is the yellowing and curling up of the leaves.

Injecting a fungicide into the bark is the best course of action.

Butternut Canker

Various kinds of butternut trees flourish in Oregon. But they can be attacked by a deadly fungus called Ophiognomonia clavigignenti-juglandacearum. In 90 percent of cases, the attack of this fungus on your tree bark results in the death of the tree.

Noticeable symptoms of the disease include cracks in the bark of branches, along with blackish fluid, loose bark, blemishes under the bark of branches and twigs, and dead twigs in the crown of the tree.

Once the fungus infects the tree, it’s incredibly challenging to stop the spread unless you get professional help. So make sure to get in touch with an expert arborist as soon as you suspect the presence of this fungus on tree bark. They can try to rescue severely infected trees by pruning off the damaged branches and getting rid of the cankers.

Black Knot

This fungal disease results in nasty swellings on the tree bark. Trees such as cherry, plum, or apricot are at high risk.

In the beginning, the swellings are greenish-brown in color. After a year, they turn black, giving your tree a monstrous appearance. One of the ways to prevent the occurrence of the disease is through regular pruning.

Black Rot


Black Knot on Tree Branch

The bark of hardwood fruit trees is at a high risk of this fungal disease. Insects, natural damage, or irregular pruning can cause wounds in the bark, making it easier for the fungus to enter. Slowly, the bark becomes reddish-brown in color. Over some time, the bark turns black and shrinks, causing it to peel off on its own.

Black rot disease can weaken the vascular system of your trees.

Beech Bark

As the name suggests, this disease affects the bark of beech trees. It’s caused due to the symbiotic relationship between Nectria fungus and European beech scale insect. At first, the beech insect attacks the bark and feeds on the sap. Once it enters inside, the fungus colonizes the bark and damages the interior. It also causes ugly cankers, oozing wounds, and blisters on the bark. Attack by this fungus can leave your tree in bad shape, making it more susceptible to other diseases.

Usually, arborists recommend strong chemical treatment protocol to contain the spread of the disease.

Cytospora Canker Disease

This fungus attacks pine, poplar, spruce, and willow trees. Trees with pre-existing root damage are more prone to attack. The first signs of this disease are noticeable in the bark of the lower branches. The infected leaves on the branches start turning purple, then brown, and ultimately die. The infected bark can also ooze a bluish-white sap.

Tried and tested methods of preventing this disease include pruning during dry weather, as there’s no effective fungicide. Since any fungus thrives in moist conditions, pruning during the dry season helps the trees to be more resistant.

Are You Wondering If Your Tree Bark Is Under Attack?

Nobody likes losing their beloved trees to a nasty fungal attack. That’s why prevention is of grave importance—ensure that you’re providing adequate sunlight and water to the trees, draining the soil properly, and sanitizing your garden tools before use.

A word of caution—managing fungal diseases is no cakewalk. Don’t attempt to fix the issues on your own. Instead, leave it to the professionals who know what it takes to help save your trees. If you suspect that your bark has been compromised due to any fungal growth, don’t waste any more time. Contact Mr. Tree right away. Our team of expert arborists can provide you with practical advice to take care of your trees.

Since we also offer pruning and tree removal services, we can handle any problem due to a possible fungal attack.