P-091 - Varying Applications of Plant Defense Activators Provide Inconsistent Control of Canker Phase and Shoot Blight Phase of Fire Blight

Fire blight caused by E. amylovora (Ea) is one of the most damaging pathogens to rosaceous plants. Streptomycin applications have been the dominant choice for controlling Ea on flowers, but options for shoot blight and canker severity control are becoming more important because streptomycin is not recommended for control at these stages  due to high risks for antibiotic resistance. Among these options, plant defense activators like Kudos and Actigard are strong materials for shoot blight and canker severity control. To expand spray program options for these phases, we explored different programs of Regalia, Actigard and Apogee at a low dosage over 5 spray applications and compared them to single to few spray applications of a higher dosages. We tested the efficacy of these materials before and after inoculation over two years. We found that Actigard sprayed 5 times at a high rate after inoculation provided good reduction of shoot blight severity (74%), canker incidence (88.5%) and canker length (91.2%) compared to untreated controls. In 2024 shoot blight severity, canker incidence, and canker length dropped to 19.9%, 30.3% and 45.9% reductions compared to untreated controls. Instead, spray applications  of Actigard before inoculation were more successful, demonstrating 29.3% control of shoot blight and 41.6% control of canker incidence. Despite inconsistent results, use of plant defense activators is a strong contender at combating Ea but more research is needed to determine which environmental, pathogen or host factors shape the differences in efficacy of these materials.