Herbicide resistant Phalaris minor in India—history of evolution, present status and its management.

The introduction and large scale cultivation of wheat cultivars which are semi-dwarf and high yielding in the north-western Indo-Gangetic Plains (IGPs) of India has led to the dominance of wheat mimicking weed, Phalaris minor Retz. Over the period, this weed has become a highly competitive and pernicious weed of wheat in rice–wheat cropping system resulting in huge yield losses. In 1978, the herbicide isoproturon was adopted on large scale to control P. minor in wheat fields and remained as most feasible option for its chemical control. However, P. minor populations have developed resistance over time as a result of continuos application of same herbicide. This herbicide resistance started from isoproturon with 0.8 m ha area to several herbicides like sulfosulfuron, clodinafop, metribuzin, fenoxaprop, pinoxaden, mesosulfuron + iodosulfuron and clodinafop + metribuzin in 7.5 m ha today. Out of 7.5 m ha, 3 m ha was observed under multiple herbicide resistance. To check the herbicide resistant P. minor populations, farmers adopted mixing post-emergence (POE) herbicides with metribuzin as well as its early POE application through fertilizer dust 2–3 days after first irrigation of wheat, and sequential application of pre-emergence (PRE) pyroxasulfone / pendimethalin / metribuzin followed by POE application of pinoxaden / clodinafop / mesosulfuron + iodosulfuron / clodinafop + metribuzin (low dose) in rice–wheat cropping zone of the IGPs of India. Therefore, considering the importance of herbicide resistance and its alarming situation in the region, this review presents the history of evolution of herbicide resistance in P. minor, its present status, management strategies and severity that causes a dent in the sustainability of wheat production under the rice–wheat cropping system of IGPs. In addition, for long-term management of resistance and maintenance of the sustainability of wheat yields, herbicides should be supplemented with integrated weed management strategies like soil solarization, crop rotation, use of crop residue management practices, growing of wheat cultivars with early crop vigour, timely application of herbicides with optimum dose, optimum seed rate, closer row spacing, use of microbial herbicides, exploring the potential use of allelochemicals and correct spray techniques are some of viable options for farmers to avoid losses from this troublesome weed and increasing wheat productivity. [ABSTRACT FROM AUTHOR]