Weed Management Efficiency of Pre- and Post-Emergence Herbicides in Direct-Seeded Rice

Abstract

Direct-seeded rice avoids puddling and transplanting, but it hands weeds a head start, and herbicides applied before and after crop emergence have become the main tool for managing them. This narrative review asks how well pre-emergence and post-emergence herbicides manage weeds in direct-seeded rice and how much weight the published evidence can bear. It draws on work on the weed flora of the system, the behaviour of soil-applied products such as pendimethalin and of foliar products with different modes of action, the role of water, tillage and crop competition, the spread of herbicide resistance, and the way efficiency itself is measured, and it reports no new data. Pre-emergence products are best seen as a way of suppressing the first flush of germinating grasses and small-seeded broadleaves, post-emergence products as a way of correcting what escapes, and neither group is complete without the other or without good water and crop management. Reported efficiency depends on weed flora, application timing, soil moisture and the definition used, so numbers from different studies are rarely comparable. Repeated use of a few modes of action has selected resistant biotypes and shifted the flora towards sedges, broadleaves and weedy rice. The review concludes that herbicides work best as part of a sequenced, integrated programme, and it lists what a comparable and decisive evaluation would report.