Morris, R.C.; Filer, T.H.; Solomon, J.D.; McCracken, Francis I.; Overgaard, N.A.; Weiss, M.J. Insects and Diseases of Cottonwood. New Orleans, LA. U.S. Department of Agriculture, Forest Service; Southern Forest Experiment Station; State and Private Forestry Southeastern Area. Gen. Tech. Rep. SO-8. 1975. 41 p.
Polyporus lucidus Leys. ex Fr. causes rot in roots and the basal stem of hardwood trees in the United States, Europe, the Phillippines, other parts of Asia, and North Africa. The fungus has been observed on cottonwood cuttings but not on established trees. However, since inoculum will be present in many sites intended for cottonwood, infection of established cottonwoods is anticipated.
If attacked, cottonwood would probably develop moderate to slight disease symptoms such as thin crowns and stunted foliage. Later, sporophores will be produced on or near the base of infected trees in late summer or fall.
These mushroom-shaped sporophores are a glossy reddish brown with a white, round margin. The undersurface is whitish with numerous small pores. The stalk is also glossy, dark red. Sporophores vary from 1 to 6 inches (2.5 to 15 cm) high and from 1 to 10 inches (2.5 to 25 cm) in diameter. Brown microscopic spores are released from the fine tubes in the undersurface of the sporophore cap. These spores are carried by wind and germinate on wood debris, stumps, or open wounds on living trees. As the fungus grows, it can penetrate the root system or collar of nearby susceptible trees. The wood decay is a soft, spongy, white rot with black spots.
No practical control is known for this disease. However, avoiding mechanical injuries to roots and tree bases, avoiding sites with known infections of natural stands, or removing infected trees helps reduce infections.
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