Importance. -- This fungus is distributed widely on oak, elm, and maple species in the East. It is common at the bases of older, living oaks in yards, parks, and along streets. While its ability to kill trees is questionable, it will decrease tree health over time.

Identifying the Fungus. -- Fruiting bodies are tan- to buff-colored conks or irregular cushions, 4 to 24 inches by 3 to 10 inches, on roots or at bases of trees. Young conks may grow around green leaves or show leaf imprints on top from where leaves lay on the growing conks. A yellowish liquid may exude from young conks, and old conks look like burned wood on top (figure 60).

Identifying the Injury. -- Thinning crowns may result from long-term infections that degrade root systems. The slow crown deterioration weakens the tree and may lead to a more serious butt rot.

Biology. -- Microscopic spores enter the tree through dead or scarred roots or through fire or logging scars at tree bases. Once extensive decay has occurred, conks are produced.

Control. -- The best control is to prevent injury (e.g., from lawn mowers and tire traffic) because the fungus enters through wounds in the bark of roots or tree bases. As with all root and butt rotters, bole and crown conditions should be monitored regularly for signs of weakening and possible breakage.