Sweet Cherry Tree Cuts: New Ways to Stop Bacterial Attack

The Pacific Northwest cherry farms face a serious threat from bacterial canker, mainly caused by two strains of Pseudomonas syringae. The bacteria infect young trees when their stems are cut during pruning, leading to rapid death of the plants. Traditional protection has relied on copper sprays, but many local bacteria have learned to ignore copper. Researchers tested several other chemicals and different pruning practices. In laboratory tests, lime sulfur at 5‑10% concentration stopped the bacteria from growing within six hours. Clove oil proved even more powerful; a tiny amount (0. 0625%) wiped out both bacterial types in half a minute.

Field experiments in 2024 compared these new treatments with copper and latex paint. When pruning happened on hot, dry days, the antibiotics kasugamycin and oxytetracycline cut down canker growth more than the other products. On cool, humid days, oxytetracycline, a product called Actigard, and kasugamycin still performed best, producing shorter cankers. The study also found that canker spread faster and more often when pruning occurred under cool, damp conditions. In 2025, the team tried kasugamycin again. It still kept cankers from expanding, but adding a vaccine-like product called Vacciplant or extra chemicals made no difference. They also discovered that removing plant tissue at least 12. 7 cm below a visible canker left no bacteria behind, suggesting deeper cuts may be safer. Overall, the results show that choosing the right chemical and timing pruning to suit weather can make a big difference in protecting sweet cherry trees from bacterial damage.

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