Sustainable weed management in direct seeded rice culture: a review.

The weed-rice ecological relationship is very complex and dynamic. Weed distribution and successions are always affected by management and environmental factors. Weed spectrum and degree of infestation in rice field are often determined by rice ecosystems and establishment methods. Due to high weed pressure, weed management in direct seeded rice has been a huge challenge for the researchers and farmers as well. Integrated weed management approach based on critical period of crop weed competition, involving different direct and indirect control measures, has been developed and widely adopted by farmers to overcome weed problem in direct seeded rice in a sustainable way. Although a number of sulfonylurea herbicides, diquat, paraquat, glyphosate quinclorac, MCPA have been found to be suitable alternatives to the old herbicides like 2,4-D, a less herbicide-dependent weed management strategy must be developed to reduce the risk of developing herbicide resistance in weeds. Weed control methods must be sought that are friendlier to the environment and substantially reduce the cost of weed management to farmers. Weedcompetitive and allelopathic rice varieties, seed priming for increased weed competitiveness, higher seeding density should be considered as a management strategy. In order to devise a sustainable weed management strategy for direct seeded rice, detailed studies need to be done on the biology and ecology of notorious rice weeds, particularly Oryza sativa L. (weedy rice), Echinochloa spp., Leptochloa chinensis (L.) Nees, Limnocharis flava (L.) Buch. Commelina benghalensis, Ipomoea aquatic, Cyperus iria and Fimbristylis miliacea.