How to Diagnose Tree Fungus


Trees are an asset to a home. They help to raise your property value, lower heating and cooling costs, prevent erosion, and improve the aesthetic appeal of your landscape. But a tree lives in a delicate balance with its surroundings that can easily be upset. If a tree's bark is damaged by regular lawn maintenance or poor pruning, it can weaken the tree and allow fungus to invade. Diagnosing fungus is the first step to restoring a tree's health.

Step 1

Walk away from a tree and observe the overall appearance. A tree that is declining in health due to fungal infection may produce a sparse canopy.

Step 2

Pick a leaf from the tree and look at it. Often, the condition of a tree's leaves will reveal symptoms of fungus problems in the tree's roots. Some fungus, such as powdery mildew, leaf spot and leaf blister, affect leaves directly. Powdery mildew produces a white powdery fungus on the leaves of trees. Leaf spot produces black, pimple-like sores on a leaf. These sores are fruiting bodies that produce new spores, while leaf blister produces light green or yellowish blister-like bulges.

Step 3

Take a cutting off a tree branch with a pair of pruning shears. Examine the twigs for evidence of fungal diseases that affect the bark, such as canker. Cankers are localized dead areas of bark that occur when fungus grows between the bark and the trunk of the tree. Cankers appear as sores in the bark of a tree that will cause the bark to rot and reveal the pith layer. Severe cankers on the limbs of trees can disfigure a tree by causing all the bark around the limb to rot away. When a tree's vascular system is interrupted this way, it is known as girdling.

Step 4

Examine the trunk of the tree for signs of fungus. Fungus in the trunk of the tree may appear as cankers in the bark, or the hollowing of the tree's trunk. The fungus may also produce a growth, known as a conk, from the trunk or cause the trunk to ooze resin. Peel back a section of bark to look beneath it. Some fungus will grow in a fan shape beneath the bark.

Step 5

Observe the ground around the tree. Mushrooms that spring up from the ground in the tree's root zones may be an indication of the presence of fungus in the roots of the tree.

Step 6

Dig around the trunk of the tree with a shovel to uncover the tree's primary roots. If these roots appear soft or rotted, this may be a sign of fungus. The presence of threadlike white or black fungus in the roots is another good indicator of the presence of fungus.

Step 7

Compare the symptoms that your tree exhibits against known symptoms of fungal infections to narrow down the list of possible fungal infections your tree may exhibit. Many books on landscaping, trees and gardening contain examples of fungal diseases as well as pictures of the diseases. A tree surgeon, arborist or your local county extension agent may also be able to confirm your diagnosis.

Things You'll Need

  • Pruning shears
  • Shovel


  • Iowa State University Extension: Diagnosing Tree Problems
  • Iowa State University Extension: Fungal Cankers of Trees
  • Ohio State University Extension: Leaf Diseases on Ornamental Trees and Shrubs
  • Washington State University Extension: Armillaria Root Rot, Shoestring Root Rot, Honey Mushroom

Who Can Help

  • Mississippi State University Extension: Ornamental & Tree Diseases
Keywords: diagnosing tree fungus, signs of fungus, plate fungus

About this Author

Tracy S. Morris has been a freelance writer since 2000. She has published two novels and numerous online articles. Her work has appeared in national magazines and newspapers, including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World."