Key Features
- Dieback or stunted branches
- Sunken or discolored bark
- Cracking or peeling of bark
Symptoms
Canker describes stem spots, lesions, discoloration and/or slight decay of an isolated area on a branch, twig, or trunk, caused by fungi or bacteria. Cankers on young and thin-barked trees and shrubs appear sunken and/or discolored. Cankers are not always visible on older thick- barked trees, but dieback from the branch tip back to the canker is a key symptom of infection. Small bumps, reproductive structures, can be seen on the surface of or along the edges of some fungal cankers. Bacterial cankers and a few fungal cankers may weep, excreting a thin liquid from cracks in the bark. Similar symptoms can be caused by insects or physical injury. Contact a plant disease diagnostic clinic for more information on submitting canker samples for analysis.
Biology
Trees and shrubs under stress are especially prone to infection and canker development. Mechanical damage (from cars, weed whips and lawn mowers), environmental injury (frost cracks, sunscald, etc.), pruning wounds and borer insects can promote infection by canker pathogens. There are different types of canker pathogens (in increasing order of severity). Annual cankers are usually minor, opportunistic pathogens that do not expand unless continued stress predisposes the plant to infection. Perennial cankers result when the host plant is unable to completely wall off the pathogen. The cankers are rarely lethal to trees but weaken their structure, predispose them to wind-damage, and detract from its appearance. Diffuse cankers are the most serious of all three cankers and result when the invading fungus grows so quickly that the main stem of the tree girdled, resulting in plant death.
Management Recommendations
Certain actions can reduce a plant's susceptibility to canker pathogens. Water trees regularly during dry periods to alleviate drought stress. Occasional fertilization will improve tree vigor on poor soils. For new plantings, select trees that will thrive in each location, paying particular attention to soil properties, water availability, and amount of sunlight. Remove any cankered branches-cut six to 12 inches below the edge of the canker for fungal cankers and up to 24 inches below in the case of bacterial cankers. Dead or dying branches should also be removed. Be sure to sterilize pruning equipment between cuts with a 10% bleach solution or 70% rubbing alcohol. Prune during dry weather to minimize the spread of the disease. In winter, wrap thin-barked trees, such as maples, mountain-ash, and crabapple to help prevent sunscald and frost cracks. Fungicides are not effective for the control of cankers.
Effective Pesticides
Pesticides are neither available nor recommended for managing this disease.
Resources
