Weed management strategies in wheat-A review

Abstract

Weed infestation is one of the major biotic constraints in wheat production. Wheat is infested with diverse type of weed flora, as it is grown under diverse agroclimatic conditions, different cropping sequence, tillage and irrigation regimes. The yield losses due to weeds vary depending on the weed species, their density and environmental factors. Among weeds, Phalaris minor Retz. is single most dominant grassy weed in northern Indian plains causing significant yield losses. For controlling weeds in wheat, growers mostly rely on herbicides due to cost and time effectiveness. For control of diverse weed flora in wheat combination of herbicides either as tank mixture, if compatible (sulfosulfuron + metsulfuron; mesosulfuron + iodosulfuron) or as sequential, if not compatible (fenoxaprop or clodinafop or pinoxaden with metsulfuron or 2, 4-D) are required. Further, the herbicide efficacy can be improved by use of adjuvants, safeners and proper spray technology. A greater focus on spray technology by imparting training to growers, field functionaries and industry personnel is required. However, sole dependence on herbicides is also not desirable as it contributes to shift towards difficult-to-control weeds and the rapid evolution of herbicide resistance, which is a threat for sustainable wheat production. Presently some of P. minor populations have shown the evolution of multiple herbicide resistance across three modes of action (Photosynthesis at photosystem II site A, ACCase and ALS inhibitor). Studies on the quantification and characterization of herbicide resistance in P. minor have revealed that some of the populations had GR50 (50% growth reduction) values for clodinafop > 12 times greater than that of the most S (susceptible) population. Population resistant to clodinafop exhibited cross-resistance to fenoxaprop (fop group), tralkoxydim (dim group)and pinoxaden (den group). Similarly, population resistant to sulfosulfuron showed cross-resistance to mesosulfuron and pyroxsulam. Management strategies must be developed to prevent selection and spread of herbicide resistant populations. For control of multiple herbicide resistant P. minor populations (resistant to isoproturon, clodinafop and sulfosulfuron) pendimethalin, trifluralin, pyroxasulfone, metribuzin and terbutryn are effective. Also, the multiple herbicide resistant populations showed sensitivity to glyphosate and paraquat. However, for efficient weed management, the non-chemical weed management tactics should be adopted in conjunction with chemicals (like herbicide mixture and rotation, optimum spray time, dose and methods). Some of the non-chemical agronomic strategies like tillage, sowing time, sowing methods, competitive crop cultivars, higher crop density, closer spacing, irrigation, fertilization, crop rotation and sanitation practices (weed-free crop seeds and manure) can be adjusted and adopted in such a manner that they provide the competitive edge to the crop over weeds. As the introduction of herbicide having new mode of action has slowed down, therefore, there is need to revive some of the old herbicides (viz. pendimethalin and trifluralin) as well as to develop wheat varieties tolerant to less selective herbicides like metribuzin and resistant to non-selective herbicides like glyphosate and glufosinate. Integration of knowledge of weed biology and non-chemical methods of weed control with chemical methods will help in increasing the life of existing herbicides and make the weed management cost-effective and efficient.