Impact of different herbicide spray fluids applied using drones on nutrient removal by weeds in transplanted rice

A field study was conducted on the efficacy of different herbicide spray fluids applied using drone and knapsack sprayer on weed density, dry weight and nutrient removal by weeds present in rice field of Wetland farm, Tamil Nadu Agricultural University, Coimbatore, during Kharif 2022. The experiment revealed that combined application of pre-emergence Pyrazosulfuron-ethyl (25 g a.i. ha-1) and post-emergence Bispyribac-sodium (25 g a.i. ha-1) using a hybrid drone with a flat jet nozzle and 37.5 L ha-1 spray fluid significantly reduced weed populations to 2.31 and 2.68 weeds m-2 at 40 and 60 days after transplanting (DAT), respectively. It also decreased weed dry weight to 2.60 and 2.99 g m-2 at the same intervals. This effective weed control is attributed to the suppression of subsequent weed germination in transplanted rice through the post-emergence herbicide application. Application of Pyrazosulfuron-ethyl (25 g a.i. ha-1) on 3 DAT as PE fb Bispyribac-sodium (25 g a.i. ha-1) on 25 DAT as PoE (H2) recorded significantly lower nitrogen, phosphorus and potassium at 40 and 60 DAT, respectively. Further, spray fluid of 37.5 L ha-1 was observed with lower nutrient removal by weeds, which might be due to lower weed density and dry weight.