Herbicides for control of metsulfuron resistant toothed dock (Rumex dentatus)

Rumex dentatus L. (toothed dock), a major broadleaf weed, is a severe problem of irrigated wheat in particularly notill conditions of the ricewheat system in India. Metsulfuron is being used for its control. However, the sole reliance on metsulfuron has led to its resistance evolution in R. dentatus. Pot bioassay studies confirmed high level of metsulfuron resistance with GR50 values ranging 74 to 98 times to that of the most susceptible population. Metsulfuron resistant (MR) populations had indicated crossresistance to other ALS inhibitor herbicides, triasulfuron, pyroxsulam, and florasulam. The readymix combination of halauxifen methyl + florasulam was also poor against MR populations. The most sensitive and resistant populations had GR50 values of 0.11 and 10.31, 1.0 and 269.5, 0.94 and 30, 1.13 and 3622.5, 0.16 and 10.14 g/ha for metsulfuron, triasulfuron, florasulam, pyroxsulam, and premix of halauxifen + florasulam, respectively. Results showed a high resistance level in R. dentatus against ALS inhibitor herbicides. In addition, a large number of populations (119) were also screened across broad herbicide groups used in wheat and 68.9 % populations exhibited ≤ 50 % control with a recommended field rate of metsulfuron 4 g/ha, indicating the widespread resistance. However, MR populations were sensitive to pendimethalin, isoproturon, 2,4D, fluroxypyr, metribuzin, carfentrazone and flumioxazin. So, these herbicides in rotation and as mixture can be used to manage ALS inhibitor herbicide resistance. However, for longterm sustainable management of herbicideresistant R. dentatus, alternative herbicides should be integrated with best agronomic practices to restrict its infestation in wheat.