Assessment of herbicide resistance in Phalaris minor and managing clodinafop-resistance with alternative herbicides

Studies were conducted to assess and quantify the level of herbicide resistance in P. minor towards major used herbicides through a field survey in 2015-16 followed by dose-response assays in 2016-17. A total of 16 P. minor populations were collected from farmer’s fields and screened against four majorly used herbicides in Haryana, viz. clodinafop, sulfosulfuron, mesosulfuron + iodosulfuron {Ready mix (RM)} and pinoxaden with its four graded doses (0X, ½X, X and 2X times of recommended dose). It was found that even at double of recommended dose, <80% mortality was observed in seven different populations under clodinafop; three under sulfosulfuron; one each under mesosulfuron + iodosulfuron (RM) and pinoxaden. These tested populations are generally categorized as resistant to highly resistant levels. Out of 16 populations, one showed multiple resistance towards ALS and ACCase inhibitor herbicides. Hence, for effective management of resistant P. minor and minimizing the probability of resistance development, field experiment with 16 different herbicide combinations was conducted during 2016-17 followed by 2019-20 to identify effective herbicide combinations for better management of clodinafop resistant P. minor. Field experiment advocated that sequential application of tank-mixed pre-emergence herbicides (pendimethalin with pyroxasulfone or metribuzin) followed by post-emergence (mesosulfuron + iodosulfuron (RM) or pinoxaden) along with their rotational application was effective against clodinafop-resistant P. minor and possibly a potent tool to minimize chances of resistance development.