Influence of Weather Parameters on Occurrence of Rice Blast in Mid Hills of Himachal Pradesh

Rice blast, caused by the fungus Magnaporthe grisea Sacc. is one of the most important rice diseases found throughout the globe. It usually damages leaves and panicles and reduces the photosynthetic area of the plant and may even lead to the death of the plant. However the disease does not develop until the favorable weather conditions prevail. Present work was undertaken to study the influence of weather parameters on rice blast in mid hill conditions of Himachal Pradesh. Field experiments were conducted during 1984 to 2012 at Palampur, located in mid hills of the Himachal Pradesh. Two varieties; Hasan Sarai and China 988 were sown on two dates (5^th and 15^th June) under upland irrigated situation. The first leaf symptoms of the disease appeared in the last week of July or the first week of August, when the mid-tillering stage synchronized with favourable weather conditions during all the years. It was observed that days with minimum temperature ≤ 20 °C, rainfall and cloud cover were important for the appearance and progress of this disease. During disease incidence, period of lower night temperature (19.1 °C), more number of days with minimum temperature ≤ 20 °C (11 days) and lower rainfall (246.6 mm) and more cloud amount (135 hrs) was observed during blast years as compared to non-blast years. It was also found that the maximum and mean temperature one week prior to disease appearance was 1.8 and 1.2 °C lower than the non-blast years indicating warmer temperature during the entire rice growing season is responsible for lower disease incidence and its further progress.