Perennial canker.
Cankers can be caused either by living organisms, including fungi and bacteria, or by nonliving things such as excessive low or high temperature or hail.
Many fungi that cause cankers normally inhabit the surface of the tree, gain entrance through natural or man-made wounds, and only cause disease when the tree is under stress. However, some fungi aggressively attack trees and cause cankers.
In the nursery, deciduous woody ornamentals should be examined for cankers. Great care should be taken to prevent injury to the trunk and branches. Pruning should be done late in the dormant season without damaging the branch collar or surrounding bark. Pruning should be done while unwanted branches are small and wounds will heal quickly. Do not prune during wet weather, nor from mid-August to leaf drop. Many canker and wood decay fungi are most active during that period.
Promote moderate tree vigor so that the tree's natural resistance to disease can be expressed and wound healing can begin promptly and develop rapidly. In the nursery...
Prevent drought and flooding.
Provide moderate amounts of fertilizer.
Prevent herbicide injury.
Prevent root and trunk injury.
Protect trees from insects and diseases that cause premature loss of leaves.
When inspecting branches and young trees for cankers, look for:
If these occur on branches, prune them off 3-4 inches below the canker. The cankers on the main trunk of saplings indicate that the entire tree should be removed. Perennial and diffuse cankers do not go away. Such cankers are present for the life of the tree which and shorten the tree's life considerably.
**Note that there are no chemicals that adequately control canker-causing fungi.
Diffuse canker (Botryosphaeria).
Prepared by Gary W. Moorman, Professor of Plant Pathology
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