Tree Diseases That Create Hazards

Certain diseases weaken tree structure and create a hazardous situation where property damage or serious bodily injury could result from falling limbs or the toppling of the entire tree. It is imperative that arborists, landscapers, and grounds maintenance personnel recognize the signs of a particular tree presenting a real hazard. Fungi, in most cases, are involved in tree diseases that result in the tree becoming a hazard. The activity of these fungi often has the following pattern:
  1. A wound occurs through pruning; wind damage; lawn mower injury; excavation for buildings, curbs, or sidewalks; and trenching for water and gas lines, as well as other human activities.
  2. The fungus enters the wound and causes a discoloration of the wood. Or a fungus can begin to rot roots directly with no wound required for entry.
  3. Enzymes produced by the fungus decay the internal portions of the trunk or limbs to release nutrients for the fungus, greatly weakening the wood fibers.
  4. Limbs die and give the crown of the tree an asymmetrical shape. Small twigs and branches may litter the ground under the tree. Wood of the internal portions of the trunk, limbs, or roots is so weakened that physical support is greatly reduced.
  5. The fungus begins to reproduce by forming a mushroom, conk, or shelf-like structure (fruiting structure in which spores are formed) directly on the limbs, trunk, butt, or root flares or on roots at some distance from the base of the tree.
  6. Larger limbs die and may fall. In the case of root rot, the entire tree may topple in a wind storm.



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