A Technical Report from The Bartlett Tree Research Laboratories
Cankers are dead sections of bark on branches or main trunks of trees. Bark may be killed by mechanical injuries or fungi and bacteria. Most fungi that cause stem cankers are restricted to bark and xylem tissue that are degraded due to the effects of toxins or secreted enzymes. Fungi that cause cankers and also extensively invade the xylem, simultaneously causing wood decay, are termed canker rot pathogens (e.g., Cerrena unicolor). Generally canker pathogens are unable to penetrate bark directly but will quickly colonize open wounds inflicted by pruning, frost injury, breakage caused by ice and snow, dead branches, branch stubs, twigs, leaf scars or, less commonly, through leaves and/or insect attack. In addition plants weakened by environmental stress (drought, water logging, salt damage) are more susceptible to attack. Canker diseases may cause extensive damage to trees when they kill all of the bark in a particular area, girdling a branch or main stem. Girdling results in death of all parts of the plant above the canker. If the trunk is affected, the entire plant may die.