Recent advances in weed management in wheat

Abstract

During 2011–2012, 696 m t of wheat was produced from 222-m ha area in the world; however, the growth rate of wheat over the years has been 1.1 % annually, which is less than the population growth rate of 1.5 %. Meeting the target of food demand for the ever-burgeoning world population will need a 1.6 % annual increase in wheat productivity, which is a challenging task going by the depletion of natural resources and climate change where weeds compete more vigorously with crop thus significantly lowering wheat production. As of today, 432 unique herbicide-resistant weeds have been registered worldwide in 65 countries infesting 82 crops. Out of these, more than 50 % (211) weeds have become resistant to wheat herbicides spanning 29 countries, where the USA and Australia have almost one third and one fifth of these resistant weeds, respectively, further complicating management strategies for these resistant weeds. Herbicides alone have not proved effective for sustainable weed management, and an integrated approach is needed to reduce the losses caused by weeds and realizing the yield potential of high-yielding, resource-responsive wheat varieties. Herbicide-resistant/herbicide-tolerant wheat is one approach, and efforts are being made to have wheat varieties tolerant to more than one herbicide (gene stacking/pyramiding) through molecular approaches. However, this will add to the cost and may not be remunerative in the long run if not used in a system exploiting all the possible means of reducing weed losses. Diversified cropping system, rotation of crops and herbicides, agronomic practices, and intercultural operations are needed to lower weed selection pressure, reducing the probability of herbicide failure. Competitive cultivars, optimum time and method of planting (no/minimum till), field preparation (exhausting weed seed bank), use of weed-free seed for planting, seed rate, straw management (preventing moisture loss and weed seed emergence), time of irrigation and fertilizer application, spraying stage of weeds, optimum dose, use of herbicides of multiple modes of action, their mixtures/sequential applications, and use of surfactants for increased weed control efficiency are major tools in managing weeds. Proper sanitation to prevent weed seed movement from field to field through farm machinery, organic fertilizers, irrigation, and farm produce can lower the spread of resistant weed seeds to other areas. Knowledge of weed biology, selection of competitive cultivars with early canopy cover, biological control measures where possible, routine field scouting and preventing weed seed formation, and collecting them at harvesting/threshing and their destruction need to be incorporated into the management strategies for sustainable weed management.