Incidence of Sheath Blight in Irrigated Rice and Associated Yield Losses in Northern India

Rice-growing districts in Uttar Pradesh, India, were surveyed during the months of July and October to record the frequency of occurrence and disease incidence of sheath blight caused by Rhizoctonia solani in paddy. A total of 180 paddy fields were surveyed at the block level of 21 districts, where almost all the rice varieties were found highly susceptible to R. solani and exhibited severe yield loss compared with low-infested fields. The district Muzaffarnagar had the highest rate of disease occurrence, while maximum disease severity was recorded in the district Saharanpur. This district also had the highest soil population of R. solani, followed by Mathura, Muzaffarnagar, Barabanki, Aligarh, Sultanpur, Mainpuri, and Rampur. The greatest relative yield loss attributed to sheath blight infestation was recorded in Mathura (40%). The yield loss was linearly correlated with soil population of R. solani and disease incidence. Disease occurrence, incidence, severity, and yield loss to paddy were all significantly greater in the area which experienced relatively higher temperatures (25 to 38°C) and relative humidity (49 to 100%) during the months of June to August. Furthermore, the fields applied with a total dose of 250 to 280 kg nitrogen/ha exhibited higher disease severity (2.9 to 3.3 score) compared with fields that received a moderate dose of 140 to 180 kg N/ha (0.9 to 1.8 disease severity score). The rice nursery fields were found almost free from the sheath blight, but the disease was quite prevalent in the paddy fields with 7.2 to 38.9% disease incidence which resulted in 14.3 to 39.7% yield loss to rice.