Clitocybe 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.

Root rot caused by Clitocybe tabescens Bres. occurs on many woody plants in the Southeastern States and elsewhere throughout the world. The disease has been observed in cottonwood plantations, but its full impact on this species has not yet been assessed.

First noticeable symptoms may be a decline of the crown and yellowing leaves, which fall prematurely or remain small and scant. On small trees, all foliage may die. White, fan-shaped mycelial fungus mats may form on the roots and root collar, causing decay. These mats extend upward between bark and wood and cause rot in both heartwood and sapwood.
Root system decayed by clitocybe tabescens.	C. tabescens fruting bodies above diseased roots.

In fall dense clusters of yellow-brown mushrooms develop at the base on the infected tree. These mushrooms are 4 to 6 inches (10 to 15 cm) high and have a broad, brown, scaly cap 1/2 to 2/3 inch (12 to 17 mm) in diameter and whitish gills. They produce wind-borne spores that germinate on exposed tissue of living or dead trees. The fungus spreads through the roots of infected trees and penetrates living roots of adjacent, healthy trees through root grafts or wounds.

Suppressed or off-site trees are apparently most subject to attack. Thus, the best control is to maintain a vigorous stand through site selection, spacing, and thinning. Site preparation should include removal of all roots that might harbor the fungus. Removal of infected trees may be of value in young stands; however, care must be taken to avoid spreading fungus inoculum.