Characterization and management of metsulfuron‐resistant Rumex dentatus biotypes in Northwest India

Abstract

Evolution of herbicide resistance in weeds is a serious threat for sustainable crop production. There were reports of poor control of toothed dock (Rumex dentatus L.) with metsulfuron‐methyl herbicide, an acetolactate synthase (ALS) inhibitor used in wheat (Triticum aestivum L.) at farmers’ fields in Northwest India. Two‐year greenhouse and field studies were conducted to (a) determine the level of metsulfuron resistance in toothed dock biotypes collected from farmers’ fields and (b) find effective herbicides for its management. Metsulfuron‐resistant toothed dock biotypes were 6.8‐ to 23.0‐fold less sensitive relative to the susceptible biotype based on resistance index values. Metabolic herbicide resistance is less likely as there was no evidence of involvement of cytochrome P450s those inhibited by malathion. The resistant toothed dock biotypes had a Trp‐574‐Leu amino acid substitution in the ALS gene. Application of premixes such as metsulfuron methyl plus carfentrazone ethyl (5 + 20 g ha–1) and halauxifen plus fluroxypyr (7.3 + 233.3 g ha–1) resulted in effective control of metsulfuron‐resistant toothed dock biotypes in screenhouse and field studies. This first report elucidating the mechanism of resistance to metsulfuron methyl in toothed dock from India will help in devising sustainable weed management approaches.