Corticium Root Rot
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Contents |
Importance
This soil-borne pathogen has a wide range of hosts and causes a white root rot of ashes and many other hardwoods and conifers. It has the potential to cause extensive damage to trees growing on poor sites, but green ash is generally less susceptible to this disease than many other species.
Identifying the Disease
The first symptoms usually include loss of vigor and thinning of crowns. Adventitious sprouts from roots or stems and small leaves may appear before the tree dies. Trees that die typically retain dead leaves until the next year. Trees with extensive white root rot are susceptible to windthrow.
Identifying the Fungus
The fungus produces very small, inconspicuous fruiting bodies on affected roots and the root collar. Fruiting bodies can be observed only with magnification. However, a white, mycelial mat, which covers the root collar and roots below the soil line, can easily be detected by removing soil from the base of the tree.
Biology
The fungus can survive on dead roots and stumps and spread to living roots. Insects may also disseminate the fungus to healthy trees. Spores released from fruiting bodies may germinate to produce hyphae that invade dead, woody tissue. The disease gradually kills roots, resulting in decline and sometimes death of infected trees.
Control
Control measures are not economically feasible in natural stands. In plantations or urban settings, diseased trees and affected roots should be removed to reduce the spread of the disease to adjacent trees. The triazole systemic fungicides show promise for reducing spread in high-valued trees.
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.
