Tianna DuPont, Bernardita Sallato, WSU Extension; Frank Zhao, WSU Plant Pathology. April 17, 2023.
Pre bloom as well as fall is an important time to consider prevention of Bacterial canker and Bacterial blast caused by Pseudomonas syringae. See Bacterial canker in Washington sweet cherries.
Pseudomonas syringae causes dead necrotic buds that fail to open in spring, collapsing floral buds during bloom as well as gumming cankers on branches and trunks.
The pathogen overwinters in cankers and buds (Ogawa and English 1991; Ogawa et al. 1995). In spring, it can colonize new leaves as they emerge from infected buds. Epiphytic populations build up when conditions are moist under a broad range of temperatures (77-86 F optimal, as low as 39 F). Rain and wind under high humidity disperse the pathogen in the fall. Leaf stomata, leaf scars, pruning wounds, freeze damaged tissue, and dormant buds can all be infection points. Stress and freezing pre-dispose trees and buds to Bacterial canker.
- Limit stress. Drought and waterlogging causing stress in young trees can increase the likelihood of bacterial canker infections.
- Be cautious about irrigation for frost protection in recently planted trees and recent training cuts.
- Remove cankers. It is important to prune out infected branches and leaders.
- Bactericidal sprays. Fall and spring applications of copper and Kasumin can reduce infections. Consider for blocks with known infections. Control has been variable study to study. Resistance if present will impact efficacy.
- In Oregon Kasumin applied at leaf fall, dormant, popcorn and full bloom reduced dead spurs (Pscheidt 2009).
- In Oregon 2 autumn applications of Bordeaux reduced dead buds (Cameron 1960).
- In Michigan spring applications of fixed copper reduced epiphytic populations (Olson 1983).
- In Australia a combination of fall and spring copper or Bordeaux sprays reduced canker formation (Wimalajeewa et al. 1991). The best treatment was 2 sprays in autumn (50-70% and 90-100% leaf fall), 1 winter and 2 pre-bloom.
- Antibiotics (Kasumin) and biologicals (Blossom Protect) applied prior to wounding reduced cankers (Lillrose et al. 2017).
- In multiple other studies applications of copper compounds and antibiotics were not effective (Ogawa and English 1991).
Bacterial canker in Washington sweet cherries. Sallato, B.C, Grove, G., Johnson, A. 2021.
Lillrose, T., Lang, G. A., and Sundin, G. W. (2017). Strategies to minimize bacterial canker in high density sweet cherry orchards. Acta Hort 1161.
Ogawa, J., and English, H. (1991). Diseases of temperate zone tree fruit and nut crops. University of California Division of Agriculture and Natural Resources, Oakland, California.
Ogawa, J. M., Zehr, E. I., Bird, G. W., Ritchie, D. F., Uriu, K., and Uyemoto, J. K. (1995). Compendium of stone fruit diseases. American Phytopathological Society, St Paul MN.
Wimalajeewa, D. L. S., Cahill, R., Hepworth, G., Scheneider, H. G., and Washbourne, J. W. (1991). Chemical control of bacterial canker (pseudomonas syringae pf. Syringae) of apricot and cherry in victoria. Australian Journal of Experimental Agriculture 31:705-708.