2024 Blossom Blast & Bacterial Canker Management
Anna Wallis, NYSIPM and Janet van Zoeren, LOF
Bacterial canker/blossom blast is a bacterial disease of stone fruits caused by Pseudomonas syringae pv. syringae. It is common to fruit growing areas of N. America, but we don’t always see it on an annual basis. This is because it is a “perfect storm” disease, which infects when there are low temperatures during bloom followed by a cool wet spring – just like we had this year in 2024. Most commonly bacterial canker infects sweet cherry trees and apricots, but this year we have heard reports of it in both plum and cherry trees. Most infections that have been reported occurred well inland from Lake Ontario, although we expect to continue to receive reports of this disease as the summer progresses.
Coincidentally, we addressed this disease in the Cornell Winter Fruit Webinar series hosted by ENYCHP, LOF, and NYSIPM in January 2024. Dr. George Sundin from Michigan State University presented on Stone Fruit Disease Management. If you are interested in learning more about identification and possible future management options for this disease, go to https://youtu.be/BhGuXvW7yN4?si=_jrsXDfa2eZtTkYm and scroll forward to time point 1:12.
Symptoms and life cycle of bacterial canker.
Symptoms of bacterial blast include:
- Cankers – found on trunk and limbs, irregular and rough
- Gummosis – typically amber in color, easily confused with normal oozing
- Blossom blast – blossom wilt and turn brown, cling to the tree
- Sour sap – a sour smell from cankers, associated with fermentation
- Stunting or dieback of branches
- Dead buds – when infected buds fail to develop in the spring
- Leaf lesions – tan to brown initial surrounded by yellow halo
- Fruit lesions – circular, brown and sunken
Life cycle
- Bacteria overwinter in infected parts of trees, including the margins of cankers and infected buds
- In the spring, bacteria multiply and ooze from infected regions
- The bacteria are then spread by wind and rain splash
- For infections to occur, weather must be conducive. This means cool and wet after bloom
- Bacteria require an opening in the plant (such as flowers and injury from frost or wind damage) and cannot penetrate intact tissue.
More information about this disease, including pictures, can be found in the Stone Fruit IPM for beginners guide (https://www.canr.msu.edu/ipm/uploads/files/StoneFruitIPM_Bacterialcanker7.pdf).
Management recommendations for bacterial canker. Bacterial canker is challenging to manage once infections are present. There is no way to cure bacterial canker infections. The best strategy is to prune out all symptomatic parts of the tree; this should be done in the middle of several dry days. Do Not prune stone fruits during cool wet weather!
In the fall, make two applications of copper, one at about 20% leaf drop, and one at 80% leaf drop (not many leaves left). You can also make a delayed dormant copper spray in the spring. Prevent future infections by planting healthy fruit trees. Choose sites with good air drainage as much as possible; this will minimize winter injury that may lead to potential infection sites. Promote good soil drainage and tree vigor. Practice good pruning to open the canopy, to achieve faster drying time and better coverage when applying pesticides.