Efficacy of Chemical Treatments and Culture Practices in Managing Cut-Wound Infections by <i>Pseudomonas syringae</i> in Sweet Cherry

Bacterial canker disease (BCD), mainly caused by Pseudomonas syringae pv. syringae (Pss) and P. amygdali pv. morsprunorum (Pam), threatens the Pacific Northwest (PNW) cherry industry. One major cause of young tree death in the PNW is heading-cut infections by Pseudomonas in newly established orchards. While copper has long been used for cut-wound protection, copper resistance in pseudomonads is widespread in the PNW. This study evaluated alternative chemicals and cultural strategies for management of cut-wound infections. Lime sulfur (LS) exhibited concentration- and time-dependent bacteriostatic activity in vitro, with 5-10% LS efficiently reducing Pss and Pam populations within 6h. Clove oil at concentrations equal to or above 0.0625% completely eliminated both pathogens within 30 s. To evaluate the efficacy of alternative chemicals, field trials in 2024 revealed that kasugamycin and oxytetracycline significantly reduced canker development when heading-cuts were performed under hot, dry weather conditions as compared with copper- and latex-paint-based treatments. When heading-cuts were done under cool, humid conditions, oxytetracycline, Actigard, and kasugamycin exhibited better cut-wound protection in terms of canker length. Canker development was more rapid and occurred at a higher frequency in trees pruned under cool, humid conditions compared to those pruned during hot, dry conditions. In 2025 field trials, kasugamycin (Kasumin) again suppressed canker progression, while addition of Vacciplant or additional chemical treatment offered no benefit. Furthermore, when plant tissues were removed at least 12.7 cm below visible cankers, no pathogen can be recovered. Our results indicate that chemical application and weather conditions during heading cut might be crucial in preventing cut-wound pseudomonads infection.