Corticium Root Rot

Morris, R.C.; Filer, T.H.; Solomon, J.D.; McCracken, Francis I.; Overgaard, N.A.; Weiss, M.J. 1975. Insects and Diseases of Cottonwood. Gen. Tech. Rep. SO-8. New Orleans, LA: U.S. Dept of Agriculture, Forest Service, Southern Forest Experiment Station. 41 p.

White root rot, or Corticium root rot, caused by Corticium galactinum (Fr.) Burt. attacks numerous woody and herbaceous perennial species in the United States, Europe, the West Indies, and Japan. Only a few cases of this disease have as yet been observed on cottonwood in plantations, but it is potentially destructive because of its wide occurrence and ability to spread from tree to tree.

Infected trees may only appear unthrifty with thin crowns. However, foliage may turn brown suddenly and die, accompanied by death of twigs and main stem. The sporophore appears on the root surface as a white or cream-colored layer of fungal growth without definite form or features and may persist for some time. The exposed sporophore surface may appear dry and cracked. Spores are wind disseminated. Under favorable conditions, they germinate and invade dead woody tissues or may even invade living root tissues. The fungus then spreads through the tissues, killing living cells and decaying the wood. Wood of affected roots often shows concentric spots, and roots may appear knotted or gnarled. Diseased trees occur singly or in small randomly located groups.

Corticium galactinum fruiting bodies on decayed roots. Photo by James Solomon, USDA Forest Service

There are no practical control measures for this disease. However, avoiding sites where native stands are known to be infected and removing diseased trees from plantations are beneficial measures. Care should be taken so that pieces of infected roots or other inoculum are not spread to other areas. Replacement of plantation trees killed by this disease is generally not effective.