Conks Figure 1 Figure 2 A conk is the external sign of wood rotting fungus. These may appear as crusts or flat "hoof-shaped" brackets   (Figure 2) on stems and branches. Conks are a sign of rot and an indication that the tree may have some serious internal defects that will affect its longevity and could result in the tree becoming a safety hazard. (Note: While the presence of conks indicates the presence of rot, it is possible that a tree will have  serious rot without conks being visible.)                                                                               Tree ProblemsTree Rot and Cavities