Written by Sheersa Manna and Frank Zhao, WSU Plant Pathology, December 30, 2025
Bacterial canker disease of sweet cherry continues to be a persistent and economically important disease of sweet cherry in the Pacific Northwest. The pathogen primarily overwinters in cankers. Removing cankers is essential to reduce the inoculum, especially in young orchards, where heading cut infection in the spring always leads to canker development as fresh pruning wounds provide direct entry points for the bacterial pathogens.
One of the most common questions growers ask is how far to cut below a visible canker to completely remove the canker and associated pathogens. A recent study found that bacteria can still be recovered 3 inches below visible canker but not 5 inches (Fig. 1), therefore, removing approximately five inches below the visible margin of a canker during hot/dry conditions can effectively remove the pathogen from further infection and limit disease spread during pruning. In addition, allowing pruning wounds to dry and heal before the onset of cool, humid, or wet conditions is an effective cultural strategy for reducing infection risk. It is also beneficial if pruning tools are sanitized after every cut as pruning tools could transfer bacterial inoculum from infected to healthy tissues, leading to new infection.
Contact
Sheersa Manna
WSU Plant Pathology
sheersa.manna@wsu.edu
Frank Zhao
WSU Plant Pathology
youfu.zhao@wsu.edu
Funding and acknowledgements
Washington Tree Fruit Research Commission, Oregon Sweet Cheery Commission and Northwest Nursery Improvement Institute
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