Importance – Irpex canker caused by I. mollis, occurs most frequently on red oaks. Incidence of this disease varies greatly in different areas. It is the least common of the canker rots, affecting only a small percentage of the trees. However, the decay under Irpex cankers extends above and below the canker face as much as 8 feet (2.4 m). The rate of decay is unknown.

Identifying the Fungus – The conks of I. mollis are 1 to 5 inches (2.5 to 12 cm) wide and creamy white, yellowing with age. They have short, jagged "teeth" on the lower surface. Conks usually occur during late summer and fall.

Identifying the Injury – Infections are associated with dead branch stubs. Irregular cankers up to 2 feet (0.6 m) long may develop. There is white rot in the heartwood behind these cankers. The canker face will have a number of sunken areas with swollen margins resulting from callous tissue formation.