Evaluation of Systemic Acquired Resistance Activators and a Plant Growth Regulator for the Management of Shoot Blight and Cankers in Pear Orchards

Shoot blight is a critical stage in the fire blight disease cycle caused by Erwinia amylovora , and management options remain limited. In 2023 and 2024, nine preventive and five curative management programs were evaluated to control shoot blight in Bartlett pears. Programs consisted of varying rates, application frequencies, and combinations of two systemic acquired resistance activators, Regalia (extract of Reynoutria sachalinensis ) and Actigard (Acibenzolar-S-methyl), and one plant growth regulator, Apogee (Prohexadione-calcium). Antibiotics and water were used as commercial and untreated controls, respectively. Young shoots were inoculated at fruit set using 10 μL of Erwinia amylovora strain Ea153N (1 × 10 9 CFU/mL). Preventive and curative sprays were applied before and after inoculation, respectively. Shoot blight severity and incidence, canker development, and fruit russet data were collected during the season. In 2023, the disease indices were higher, and only the antibiotic sprays significantly reduced shoot blight incidence and severity, whereas canker severity was significantly reduced by antibiotics and two applications of Apogee. In 2024, the program consisting of antibiotics, three applications of Regalia, and two applications of Apogee resulted in lower shoot blight severity and no cankers; however, the differences were not statistically significant. Curative applications did not reduce shoot blight or canker severity in either year. These results suggest that effective shoot blight management relies on preventive applications, with antibiotics providing the most control under high disease pressure. Alternative products may contribute to integrated management programs but are unlikely to provide sufficient control when applied alone under high infection conditions.