Fungal diseases on trees can be relatively harmless yet unattractive, or they could severely impact the health of the tree. The severity depends on many factors, including overall tree health, the type of fungus, and other diseases and pests that are common in your area.

Common Fungal Diseases

Although there are many types of fungus that can affect your tree, they all usually present in one of four ways:

  • Root rot: Fungus infects the roots or the portion of the trunk below the soil line. Since root rots can occur over long periods before they are noticed, the tree usually dies.

  • Foliage disease: Foliar fungal issues can present as white, gray, or black powdery growth on leaves and shoots, or as discolored spots on leaf surfaces. These are some of the easiest to diagnose and treat.

  • Vascular fungus: Vascular infections occur when a fungus enters the vascular system of the tree, which is where nutrients and moisture are carried from the roots to the canopy. These fungal diseases spread quickly and almost always result in death.

  • Canker-forming fungus: Cankers occur when a fungus infects the bark, usually through a cut or recently removed branch. The bark becomes sunken and sometimes appears wet or slimy. There may even be visible mushroom-like fruiting bodies present.

Of the four types of fungal infections, foliar and canker-forming varieties are often curable, while the others usually mean it is time to remove the tree.

Common Treatments

In the case of foliar fungus, a combination of fungicidal tree sprays and proper cultural care can often solve the problem. These fungi tend to flare up during moist, warm weather, so they may also clear up on their own as the weather changes. Canker-forming fungus is best avoided, generally by pruning properly and using clean tools. Once a tree is infected, you may be able to prune off an infected branch if it isn't on the main trunk. Otherwise, keeping the tree healthy may enable it to fight off the fungus on its own.

Following the watering and fertilizer schedule recommended for the tree type and your climate will help your tree remain healthy enough to fight off any fungal infections. Consult with a local tree service company if you aren't sure what the recommendations are in your area.

Pruning for Prevention

Proper pruning can prevent many fungal diseases. First, you want to trim out dead or damaged wood in late winter every year, otherwise the wood may harbor fungal spores. Make sure the pruning tools are disinfected by dipping them in a 10 percent bleach solution after every cut.

Next, treat all major cuts, such as the removal of larger branches, with a specially formulated tree paint. This provides a temporary seal over wounds so fungal bodies can't invade the tree. Finally, clean up the area around the tree after pruning. This prevents spores from surviving in the soil. For the same reason, you should always rake up fall leaves. Otherwise, fungal spores may overwinter in the leaf piles and then invade your trees after late winter pruning. 

For help with tree trimming, contact a business like Trees Unlimited. These professionals should also know how to prevent and treat tree fungus among other tree-related problems.