Control of broad-leaved weeds in wheat under eastern sub-Himalayan plains

A study was undertaken during winter seasons of 2016–17 and 2017–18 at Uttar Banga Krishi Viswavidyalaya, Coochbehar, West Bengal to assess the comparative efficacy of various herbicides and to identify the effective herbicides for controlling broad-leaved weed flora in wheat. The experiment was laid out in a Randomized Block Design (RBD) with eleven herbicides combination viz. halauxifen-methyl ester+ florasulam 40.85% WG + polyglycol; metsulfuron methyl 20 WG + surfactant; carfentrazone 40 DF; 2,4-D Na 80 WP; 2,4-D E 38 EC; metsulfuron + carfentrazone +surfactant; 2,4-D-Na + carfentrazone; 2,4-D E + carfentrazone, halauxifen-methyl + florasulam+ carfentrazone + surfactant including a weedy check and weed free treatment. It was revealed that Polygonum alone constituted almost 72% of the total broad leaved weed population in both the years. Among the herbicidal treatments, metsulfuron + carfentrazone + surfactant recorded significantly lesser weed population (10.0 and 2.3/m² during 30 and 60 days after spraying of postemergence herbicides, respectively) vis-a-vis weed dry weight (11.2 and 4.5 g/m² during 30 and 60 days after spraying of post-emergence herbicides, respectively). This combination also recorded the highest broad leaf weed control efficiency (90.1 and 99.0% at 30 and 60 days after spraying, respectively) with the lowest weed index 6.0.The new molecule halauxifen-methyl ester + florasulam in combination with carfentrazone recorded 88.1 and 94.0% weed control efficiency. It was noted that Polygonum was killed by halauxifen-methyl ester + florasulam 40.85% WG + polyglycol, but it could not control Physalis minima, the second most important weed after Polygonum. Weed free treatment mrecorded significantly higher grain yield (5.39 t/ha) followed by metsulfuron + carfentrazone + surfactant treated plots (5.04 t/ha), the best performed treatments among various post-emergence herbicides combination used in the experiment. According to the linear regression, wheat crop was likely to produce very poor grain yield (less than 1.50 t/ha) when weed biomass exceeds 400 g/m².