Weed Management in Direct-Seeded Rice Under Cambodian Conditions

In Cambodia, the increasing scarcity of rural labour is pushing farmers to find ways to manage large rice fields with meagre resources and continuously emerging crop management constraints, especially for weed control. Out-migration of rural labour has resulted in a shift from manual transplanting to direct-seeded rice (DSR) and this has changed the spectrum of weed species and made weed management more difficult in rice. This publication describes important weeds of rice in Cambodia, weed seed contamination in rice seed for sowing, weedy rice contamination in paddy and options for Integrated Weed Management (IWM). The elements of IWM include: cultural practices; stale seedbed; crop establishment methods; crop rotation; water management and chemical weed control. Modernisation of weed management in Cambodia, is constrained by a lack of uptake of existing published research and failure to incorporate results of new research into extension media. Multiple conflicting messages emanating from Donors and Non-Governmental Organisations (NGOs) also confuse farmers and delay adoption of good agricultural practices (GAP). Furthermore, in the absence of a functioning public extension service, Cambodian farmers are locked into pesticide-reliant practices and limited use of alternatives. Pesticide manufacturers, distributors and local sellers reinforce pesticide-based recommendations as the dominant technology. In Cambodia, weed research priorities include development of: management practices to reduce weed seed banks in direct-seeded rice fields; integrated weed management strategies to delay or avoid development of herbicide resistance in major weed species in direct-seeded rice; options for the integrated management of weedy rice (Oryza sativa f. spontanea) in direct-seeded rice; and comparison of Unmanned Aerial Vehicles (UAVs) with ground application for efficacy and safety of herbicide application in rice.