Non suitability of tembotrione and topramezone for weed management in sorghum [Sorghum bicolor (L.) Moench]

A field experiment was conducted during rainy (Kharif) seasons of 2019 and 2020 at Hagari, Karnataka, India to assess the efficacy of post-emergence application (PoE) of two HPPD (p-hydroxy-phenyl-pyruvate dioxygenase) enzyme inhibitive herbicides, viz. tembotrione and topramezone in combination with pre-emergence application (PE) of atrazine. Among the 10 treatments tested, atrazine 1000 g/ha PE followed by fb) atrazine 1000 g/ha PoE or 2,4-D Na salt 937.5 g/ha PoE or 2, 4-D Ethyl Ester 2368 g/ha PoE at 20 days after sowing (DAS) proved as effective as weed free treatment (hand weeding twice) in increasing the sorghum grain yield and net returns. The topramezone 37.5 and 56.3 g/ha PoE though provided effective weed control, caused phytotoxicity to sorghum resulting in 21 and 39% grain yield reduction and 32 and 74% net return reduction, respectively when compared to atrazine PE applied alone which recorded grain yield of 2.31 t/ha and net return of ^45,007 but it was better than weedy check. The tembotrione 70.3 and 105.5 g/ha PoE also caused reduction of 2.1 and 3.3% in biological yield, 18.6 and 26.1 in grain yield and 19.2 and 63.9% in net returns, respectively and was significantly inferior to weedy check. The crop phytotoxicity of tembotrione resulted in negative herbicide efficiency index (−0.09 to -0.78) and high weed index values (37.32 to 51.7) indicating its non-suitability for use in sorghum. The uncontrolled weeds (weedy check) on an average have caused 32.1, 42.7 and 32.5% reduction in biological yield, grain yield and net returns, respectively when compared to weed free check.