Integrating weather indices with field performance of novel fungicides for management of late blight of potato (Phytophthora infestans) in North Eastern Himalayan Region of India.

The hemibiotrophic fungus-like oomycete phytopathogen, Phytophthora infestans (Mont.) de Bary, causing late blight disease of potato, is one of the most serious foliar diseases of potato. The pathogen spread very rapidly and can infect at any stage of crop growth.The field experiments were carried out during winter (rabi) season of 2020-21 and winter (rabi) season of 2021-22 to find out the correlation between the disease progress and environmental factors and the effective novel fungicides registered under Central Insecticide Board and Registration Committee (CIB&RC) against P. infestans. Results revealed that T7: Mandipropamid 23.4% SC @ 0.1% (1.0 ml/L) at 35 & 55 days after sowing (DAS) and Ametoctradin 27% + Dimethomorph 20.27% SC @ 0.1% (1.0 ml/L) at 45 & 65 DAS recorded least average per cent late blight disease incidence (PLBDI) of 13.00 and 9.33, per cent late blight disease severity/index (PLBDS) of 8.81 and 5.96 and maximum tuber yield of 21.58 and 21.86 t/ha with highest benefit cost ratio (BCR) value of 1:1.95 and 1: 1.99 as compared to control during winter (rabi) season of 2020-21 and winter (rabi) season of 2021-22, respectively. T7 exhibited minimum Area under the Disease Progress Curve (AUDPC) value during both the consecutive seasons. The disease is positively correlated with maximum and minimum temperature, morning and evening relative humidity and sunshine hours. Linearity assumption scatter matrix indicates coefficient of determination of 0.916 was calculated using the pooled data.The relative potato tuber yield loss ranged from 7.38 to 19.96% and 7.14 to 19.62% during 2020-21 and 2021-22, respectively. Spray schedule with contact fungicide followed by systemic/translaminar + contact fungicide recorded reduced potato late blight disease with highest BCR value under natural epiphytotic condition.