Dynamics of Rice Brown Leaf Spot Disease (<em>Bipolaris oryzae</em>) Incidences Due to Seasonal Weather Differences in the Dry Zone of Sri Lanka

Weather factors are key determinants in ecological disease management in sustainable agriculture, while judicious crop management systems deliver better control over rice diseases in tropical conditions. This study was designed to explore the effect of weather factors under different crop management systems and seasons on Rice Brown Leaf Spot (RBLS) disease incidences caused by Bipolaris oryzae in the tropical dry zone of Sri Lanka. The incidence of RBLS was measured under Conventional, Reduced, and Organic crop management systems commencing from the first occurrence of disease symptoms, at three-day sampling intervals in the tropical dry zone during wet (Maha) 2018/19 and 2019/20, and dry (Yala) 2019 and 2020 seasons. Secondary data on weather parameters were collected from the regional weather station. The RBLS incidences were highest in the wet season and were most abundant at the reproductive stage. The disease incidence dynamics over time were found to be similar among all the crop management systems in three seasons. The cumulative amount of rainfall seven days before the disease observation (RF7), the day-RH (DRH), and the maximum (TMAX48) and average temperature (TAVG48) that were recorded 48 h before the disease observations were found to be significantly correlated with the disease incidence of crop management systems in the wet season. DRH and minimum temperature (TMIN72) of 72 h before the disease observed in the wet season resulted in higher disease incidences. The RBLS disease can be managed concerning the crop management systems under high DRH and TMIN (20-25 ℃) in the wet season.