A Case Study on the Rapid Spread of Fire Blight Due to Hail and Continuous Rainfall

Fire blight, a bacterial disease caused by Erwinia amylovora, affects fruit trees and can be transmitted between orchards over distances up to 10 km, primarily through infected seedlings or contaminated equipment. Within a 1 km radius, natural infection may occur via insect vectors, rain, and mechanical wounds. In 2023, an outbreak in the Andong region was characterized by rapid spread, with most apple orchards in an isolated village becoming affected. Two factors appear to have contributed to the rapid dissemination of the disease. First, the presence of infected apple trees within the orchards served as a local source of inoculum. Second, a high frequency of rainy days-16 in June and 19 in July-coupled with three hailstorms, notably on June 11th and 29th, likely facilitated pathogen entry through wounds on apple leaves and fruits. This case demonstrates that simultaneous occurrences of rain and hail can accelerate the spread of fire blight, suggesting that immediate antibiotic treatment following hail-induced injuries may be critical in minimizing disease incidence.