Efficacy of alternative herbicides for managing metsulfuronmethyl (ALS inhibitor) resistant Rumex dentatus L. in wheat (Triticum aestivum L.) under the north-western Indo-Gangetic Plains

Rumex dentatus L. (Toothed dock) is a dominating broadleaf weed of irrigated wheat in the rice-wheat cropping system of north-western India. For more than 15 years, metsulfuron-methyl (Group B/2 herbicides, ALS (acetolactate synthase) inhibitor) has been used for effective control of this weed. Recently, reports from farmers’ fields indicated poor efficacy of metsulfuron-methyl against R. dentatus due to herbicide resistance, potentially causing significant yield losses in wheat. Therefore, a field study was conducted during the Rabi seasons of 2017-18 and 2018-19 at the research farm of Krishi Vigyan Kendra (KVK), Chaudhary Charan Singh (CCS) Haryana Agricultural University, Panipat, India to identify alternative herbicides against R. dentatus in a field with a known history of poor control with metsulfuron-methyl. The findings revealed that metsulfuron-methyl (4 g ha-1), mesosulfuron + iodosulfuron (14.4 g ha-1) and sulfosulfuron + metsulfuron (32 g ha-1) showed poor performance in terms of percent control (16.5, 34.3 and 19.6 % respectively), density (54.1, 42.6 and 52.1 plants m-2 respectively) and dry matter accumulation (8.18, 6.31 and 9.11 gm-2 respectively) of R. dentatus along with significant reduction in yield attributes and yields of wheat. Among the pre-emergence herbicides, pendimethalin (1000 and 1500 g ha-1) was found most effective in terms of percent control (95.7 and 98.0 % respectively), density (2.8 and 1.3 plants m-2 respectively) and dry matter accumulation (0.48 and 0.12 g m-2 respectively) of R. dentatus with higher yield attributes and grain yield (5822 and 5957 kg ha-1) of wheat. Among the post-emergence herbicide, 2,4-D ester (400 and 600 g ha-1), 2,4-D Na (1000 g ha-1), carfentrazone + metsulfuron (25 g ha-1), carfentrazone-ethyl (20 g ha-1) and 2,4-D amine (750 g ha-1) were found effective against metsulfuron-methyl resistant R. dentatus.