Symptoms The first indication is usually poor growth of the shoots together with premature dropping of the leaves. One part, side or section of the tree may be affected at first. This corresponds to the side that is supported by the roots first attacked by the fungus. Trees may live for a number of years before finally dying. White mycelial plaques or fans can be seen on the main roots or root crown when the outer bark is removed. Rhizomorphs may also be found clinging to the bark in this area. These appear as dark-brown-to-black, branching, root-like structures.
Reference Miller, P.W. 1945. Diseases of filbert in the Pacific Northwest and their control. Oregon State College Station Bulletin 428.