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This guide is designed to assist Cambodian agricultural advisers to accurately identify weeds in cropping situations so that recommendations for weed control can be made based on the principles of Integrated Weed Management (IWM). Weed species differ in their responses to management practices because they have different life cycles and nutrient requirements and different modes of reproduction. They also vary in their responses to cultivation and susceptibility to herbicides. It is therefore important for the adviser and farmer to be able to accurately identify different weed species and to understand their individual weaknesses. This Guide for identification of weeds in Cambodia has been produced for that purpose. Species are arranged in alphabetical order in the Guide according to family, genus and species. A plant family (e.g. Euphorbiaceae) contains a number of related plants, all of which have one or more features in common. Families are split into a number of genera (e.g. Euphorbia, Jatropha, Ricinus), with the plants in these generic groups having further common characteristics. Each of the genera (genus) comprise one or more species, each with its own distinguishing or specific name (e.g. Euphorbia heterophylla L., Jatropha gossypiifolia L., Ricinus communis (Moq.) Gomez). These names are distinct from each other and from those of every other plant species. The Guide also includes the Khmer name for the weed, if known. A brief description, using taxonomic terminology, based primarily on the Flora of China, is given for each species. The descriptions in this Guide focus on plant habit, inflorescence, seeds and habitats that the weeds are found in.

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.