Varnish Fungus Rot
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Importance
This pathogen causes a serious rot of the lower bole and roots of green and white ashes throughout North America. Ganoderma lucidum can kill even the largest trees.
Identifying the Disease
Trees affected by varnish fungus rot exhibit yellowing, wilting, or undersized leaves and dead branches. Affected wood of the lower bole becomes soft, spongy, and light colored in advanced stages of decay, increasing susceptibility to windthrow. Identifying the Fungus. - The fungus produces annual, reddish-brown basidiocarps, singly or in clusters and with or without stalks, often near the bases of trees. The upper surface has a smooth, lacquered appearance and a distinct, lighter margin that turns darker with age. The undersides of basidiocarps have a white, porous surface when fresh. However, basidiocarps do not necessarily indicate extensive decay or imminent death.
Biology
Brown spores released from basidiocarps are dispersed throughout the summer during humid periods. Wounds on root flares and the lower bole are primary infection courts. Spores germinate and produce mycelia that attack the sapwood of all major roots and the butt section of the bole. Tree vigor may decline as decay of the sapwood advances. Rates of decay appear to be determined by tree vigor, which is often influenced by environmental stresses.
Control
In urban settings, phenoxy-types herbicides applied in lawn fertilizers can sometimes predispose trees to varnish fungus rot. Cultural practices to reduce drought, water stress, and wounding are recommended.
References
Solomon, J.D.; Leininger, T.D.; Wilson, A.D.; Anderson, R.L.; Thompson, L.C.; McCracken, F.I. 1993. Ash pests: A guide to major insects, diseases, air pollution injury and chemical injury. Gen. Tech. Rep. SO-96. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 45 p.
