Summary written by B. Sallato, C. Serban and Y. Zhao, WSU, Updated 2024. From: Sallato C., Grove G. and Johnson, A. Washington State University. FS366E Washington State University Extension Publication. Pullman, WA, USA. DOI: https://doi.org/10.7273/000001731
Bacterial canker in sweet cherries is caused by the bacterium Pseudomonas syringae pv. syringae (PSS) van Hall (Romoli, 1963, Latorre et al., 1980). This pathogen is commonly associated with wet and cold weather (Latorre, 2008). The pathogen P. syringae can colonize any plant tissue without provoking infection or symptoms. However, the bacterium requires a wound or a natural opening, accompanied by wet conditions or standing water, to infect the trees. As a result, autumn becomes a critical period for preventive management.
Symptoms in Sweet Cherry
The most distinct symptoms of bacterial canker in sweet cherry is a dark canker, often accompanied by gummosis (reddish-brown exudate) (Latorre, 2008, CABI, 2020) (Figure 1). Symptoms commonly develop at the base of trees, particularly in younger trees, which are more susceptible to damage by machinery, rodents, frost, and irrigation. These factors provide ample opportunity for PSS infection to occur.
Figure 1. Gummosis due to bacterial canker in sweet cherry (photo: C. Serban), dormant wood with bacterial canker in spurs (photo: B. Sallato).
Management Recommendations
- Early Defoliation: Leaf drop creates a natural wound, which can become areas of infection for the pathogen. Promoting early defoliation while conditions are dry and warm reduces the risk of infection (see more in Early Fall Defoliation in Sweet Cherry).
- Prevent Damage: Avoid damaging trees during wet conditions, especially during tasks like weeding, pruning, or any mechanical wound, as this increases the risk of infection.
- Weed management: Given that weeds can host PSS, adequate weed management will reduce the risk for disease transmission.
- Pruning: Prune and remove infected tissues during dry weather, cutting below visible canker. To prevent transmission with pruning tools, consider removing the cankers before your regular pruning.
- Severely Infected Trees: Remove severely infected trees to reduce spreading the disease.
- Frost Protection: Pseudomonas syringae is an ice nucleating bacterium, which can freeze cellular water at warmer temperatures. Protecting trees from freezing temperatures reduces the risk of damage.
- Copper Resistance: In many regions of US and the world, copper-resistant strains of the bacterium are present, making copper sprays ineffective.
Additional information
- Pscheidt JW and Ocamb CM. 2021. PNW Plant Disease Management Handbook. https://pnwhandbooks.org/plantdisease/host-disease/cherry-prunus-spp-bacterial-canker.
- Crop protection guide for tree fruit in Washington. Washington State University EB04119. https://cpg.treefruit.wsu.edu/cherry-programs/overview/#pests_disease
- Sallato C., Grove G. and Johnson, A. Washington State University. FS366E Washington State University Extension Publication. Pullman, WA, USA. DOI: https://doi.org/10.7273/000001731
- Cherry: Bacterial canker | Hortsense | Washington State University.
Contact
Bernardita Sallato
Tree Fruit Extension Specialist
b.sallato@wsu.edu
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