Cutting the shelf reveals a reddish-brown center. The underside of the shelf is brown with millions of tiny pores in which the spores are formed. A sure sign of severe damage to the tree is the presence of the fruiting structures. Infected trees should be removed immediately. The underside of the fruiting structure has millions of tiny pores in which the spores are formed.
New shelves form on the wood the following summer and autumn.
The bark where the fruiting structure forms is slightly depressed and cracked. Fruiting structures form long after most of the damage has been done. Infected trees are very prone to wind breakage even before the fungus begins to form fruiting structures and should be removed at the first sign of infection. Trees with iron chlorosis and those under other stresses are most severely affected. Little damage results from this disease.