Bio-efficacy and Phytotoxicity of New Generation Fungicide Trifloxystrobin 25%+Tebuconazole 50 % WG against Blast of Rice in New Alluvial Zone of West Bengal, India

Abstract

Disease severity of rice blast was assessed on 15 tagged hills per replication using the Standard Evaluation System (0–5 scale). Disease scores were recorded at the time of the first fungicidal application (day 0) and subsequently at 3, 5, and 7 days after spraying (DAS). The same assessment schedule was followed after the second fungicidal application (10 days after the first spray), with observations recorded at 3, 5, 7, and 10 DAS. Phytotoxicity was evaluated simultaneously using a 1–10 rating scale based on visual symptoms such as chlorosis (yellowing), necrosis, leaf injury, wilting, epinasty, hyponasty, vein clearing, and stunting after both sprays. Disease severity was low at the time of the first fungicidal application and did not differ significantly among treatments. Following the second spray, all fungicidal treatments effectively suppressed blast severity compared with the untreated control. Among the tested treatments, Trifloxystrobin 25% + Tebuconazole 50% WG @ 800 ml ha⁻¹ provided the maximum reduction in Percent Disease Index (PDI) and was statistically comparable with the standard check, Galileo (Picoxystrobin 25% SC @ 600 ml ha⁻¹). The efficacy of the fungicide was reflected in its sustained suppression of disease progression throughout the observation period. Trifloxystrobin 25% + Tebuconazole 50% WG was further evaluated for its effect on grain yield and phytotoxicity under field conditions. The fungicide significantly increased grain yield over the untreated control, with the 800 ml ha⁻¹ dose producing the highest yield increase (17.95%) and performing on par with the standard fungicide. No phytotoxic symptoms were observed on rice plants at any of the tested doses, including the highest dose of 1200 ml ha⁻¹, indicating that the fungicide is safe for crop application under field conditions.