Studies on the epidemiology of white rust and Alternaria leaf blight and their effect on the yield of Indian mustard

High severity of white rust and Alternaria leaf blight diseases is an important constraint in the production of Indian mustard. An experiment was conducted at the Regional Research Station, Gurdaspur during Rabi, 2011 to 2012 to investigate the role of weather conditions like humidity, temperature and rainfall on these diseases and to measure the loss in yield due to them. The first visible symptoms of white rust first appeared 42 days after sowing while those of Alternaria leaf blight appeared at 61. The development of white rust and Alternaria leaf blight was favoured by a mean temperature ranging between 11.4 to 17.7°C and 13.5 to 19.3°C, respectively along with an average relative humidity of more than 70%. A highly significant positive correlation was observed between disease severity as well as maximum and minimum temperatures. The average loss in seed yield due to these diseases was estimated to be 36.88%.