Epidemiology of Alternaria blight caused by (Alternaria tagetica) of marigold under Punjab conditions

Marigold (Tagetes spp.) is one of the most common traditional flower crops grown, commercially in different parts of India. The present studies were carried out to investigate the epidemiology of Alternaria blight caused by Alternaria tagetica of marigold. An extensive survey was conducted in five different districts of Punjab state namely Pathankot, Ludhiana, Patiala, Bathinda and Mansa. The study revealed that disease was prevalent at all the locations and percent disease incidence varied from 13.33 to 29.33per cent and 11.78 to 22.67 per cent during 2022 and 2023 respectively. Maximum disease incidence was observed in Pathankot and minimum in Mansa in both the years. It was observed that weather parameters played an pivotal role in development of disease, as minimum temperature, evening humidity and rainfall showed positive correlation with the disease progression. Whereas, maximum temperature, morning humidity and bright sunshine hour showed negative correlation with the development of disease. The AUDPCs were calculated directly from data and an estimation of the AUDPC from two data points provided an equivalent amount of information as from repeated assessments. Step wise regression was found to be highly significant with the observed DI (R ² = 0.99, Multiple R = 0.99) and PDI (R² = 0.99, Multiple R = 0.99) data. The model efficiency was further evaluated using Nash Sutcliffe efficiency (NSE). This model will help in timely disease forecasting and will guide in optimized fungicide use to minimize crop losses.