Epidemiology and seasonal incidence of Powdery Mildew (Phyllactinia corylea) in mulberry under eastern dry zone conditions of Karnataka

Abstract

Powdery mildew of mulberry caused by Phyllactinia corylea is an emerging foliar disease affecting sericulture in the Eastern Dry Zone of Karnataka. The present investigation was undertaken to assess the distribution, severity and epidemiological behaviour of the disease during Rabi 2024–25. A roving survey conducted across major mulberry-growing districts revealed considerable spatial variation in disease incidence and intensity. Among the surveyed districts, Kolar recorded the highest mean disease incidence (43.33%) and Per cent Disease Index (PDI) (31.94%), followed by Chikkaballapur (37.50% incidence; 24.37% PDI) and Ramanagara (35.83% incidence; 22.55% PDI). Bengaluru Rural (30.83% incidence; 17.85% PDI) and Tumakuru (23.33% incidence; 14.24% PDI) exhibited comparatively lower disease pressure. Based on PDI values, Kolar, Chikkaballapur and Ramanagara were categorized as severely affected (Grade IV), whereas Bengaluru Rural and Tumakuru were moderately affected (Grade III), indicating non-uniform disease distribution influenced by local agro-climatic conditions and crop management practices. Epidemiological studies conducted on the susceptible variety V1 at Chintamani demonstrated a progressive increase in disease intensity with crop age. The highest PDI (43.59%) was recorded at 84 days after pruning, coinciding with moderate maximum temperature (26–28°C), high relative humidity and absence of rainfall. Correlation analysis indicated a positive association of disease intensity with maximum temperature (r = 0.564) and wind speed (r = 0.156), while negative correlations were observed with minimum temperature, relative humidity and rainfall, with rainfall showing the strongest negative relationship (r = −0.611). Multiple regression analysis explained 83.7% of variation in disease intensity (R² = 0.837). The Area Under Disease Progress Curve (AUDPC) values increased sharply during 63–84 days after pruning, highlighting this period as critical for epidemic development. The findings emphasize the importance of timely monitoring and targeted management during mid to late crop stages to minimize yield losses.