What is Nectria canker? Nectria canker is a common and potentially lethal disease that affects many species of trees and shrubs. This disease can cause significant damage on newly planted, as well as established, trees and shrubs that are under stress.
What does Nectria canker look like? Nectria canker is characterized by the formation of sunken areas (cankers) that form on twigs, branches, and trunks. Cankers can form at leaf scars and wherever injuries occur. Injuries can be caused by pruning (particularly improper pruning), frost, hail, cracking from heavy snow or ice, sunscald, insects, or animals. Cankers appear first as slightly sunken areas on the bark, but can grow for years, becoming target-shaped or elongated. Small branches girdled by cankers can wilt suddenly, fail to leaf out, and die.
Where does Nectria canker come from? Nectria canker is caused by two fungi, Nectria cinnabarina and Nectria galligena. These fungi survive in the margins of cankers where they produce numerous fruiting bodies (reproductive structures). Fruiting bodies can be cream, coral, orange, or red, and eventually darken to brown or black with age. Spores are dispersed by wind, water, and pruning tools. Cankers expand slowly, usually when the host is dormant or under stress. Infected plants may hold the fungus in check by producing wound-closing (callus) tissue around the infected area.
How do I save a tree with Nectria canker? There is no cure for Nectria canker. Remove smaller branch cankers by pruning six to eight inches below the canker. Disinfect pruning tools after each cut by treating them for at least 30 seconds with 10% bleach solution or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants). If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting. Trees with trunk cankers may live many years with the disease. Healthy trees are better able to slow the development of Nectria canker, so make sure that trees are watered and fertilized properly.
How do I avoid problems with Nectria canker in the future? Choose plants that are well-adapted to your local climate. Avoid any stresses to your trees and shrubs. Prune trees and shrubs properly. See UW-Garden Facts XHT1014, Pruning Deciduous Trees, and XHT1015, Pruning Deciduous Shrubs), and avoid injury to root and trunks from lawnmowers. Remove grass from around the base of trees and shrubs, mulch properly, and water as needed to avoid drought stress.
For more information on Nectria canker: See UW Bulletin A3281, Honey Locust Disorder: Canker Diseases in Wisconsin (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.
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