Most plant diseases cause a loss of yield or damage the aesthetic qualities of the infected plant. Certain diseases of trees, however, weaken their 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 that a particular tree may present a real hazard.
Some fungi and their hazards are introduced in datails in the attached file, such as: Armillaria species, Fomes fomentarius, Ganoderma lucidum, Ganoderma applanatum, Inonotus dryadeus, Laetiporus sulfureus.
Gary W. Moorman (Professor of Plant Pathology at Pennsylvania State University): Tree Diseases that Create Hazards,
http://extension.psu.edu/plant-disease-factsheets/all-fact-sheets/hazard-trees