The fungus Eutypella parasitica attacks maples and boxelder causing large perennial cankers on trunks or main branches. On sugar and Norway maple, eutypella cankers are elongate with conspicuous ridges of callus tissue around the sides (Figure 14). On sugar maple these cankers seldom girdle the stem but the enlarged, distorted growth around the canker and subsequent exposure of wood to decay fungi may structurally weaken the tree. On Norway maple, eutypella stem cankers can completely encircle the trunk causing top dieback. Cankers on Norway maple are often associated with frost crack or winter sunburn of the lower trunk.