Weed Ecology and Weed Management Strategies for Dry-Seeded Rice in Asia

Rice is a principal source of food for more than half of the world population, and more than 90% of rice worldwide is grown and consumed in Asia. A change in establishment method from manual transplanting of rice seedlings to dry-seeded rice (DSR) has occurred in some countries as growers respond to increased costs or decreased availability of labor or water. However, weeds are a major constraint to DSR production because of the absence of the size differential between the crop and the weeds and the suppressive effect of standing water on weed growth at crop establishment. Herbicides are used to control weeds in DSR, but because of concerns about the evolution of herbicide resistance and a scarcity of new and effective herbicides, there is a need to integrate other weed management strategies with herbicide use. In addition, because of the variability in the growth habit of weeds, any single method of weed control cannot provide effective and season-long control in DSR. Various weed management approaches need to be integrated to achieve effective, sustainable, and long-term weed control in DSR. These approaches may include tillage systems; the use of crop residue; the use of weed-competitive cultivars with high-yield potential; appropriate water depth and duration; appropriate agronomic practices, such as row spacing and seeding rates; manual or mechanical weeding; and appropriate herbicide timing, rotation, and combination. This article aims to provide a logical perspective of what can be done to improve weed management strategies in DSR.