Weed management challenges in rice (Oryza sativa L.) for food security in Bhutan: A review

Rice is the most important and staple cereal in Bhutan, currently grown over an area of 19,549 hectares with a total production of 77,038 tonnes. However, its yield is limited in certain regions due to weed competition with losses of up to 50% reported through infestation from both annual and perennial weeds. In this article, we describe the current weed management practices in rice in Bhutan and identify challenges and prospects to guide future weed control research given that weed science in Bhutan is in its infancy. Generally, the most common form of weed control is hand weeding. However, herbicide use is also increasing as farmers face labour shortages on farms and realize the benefits of herbicides, especially in reducing the time taken to weed crops. But the continued use of the single chemical butachlor is a concern given the possible development of herbicide resistance. Research priorities for weed management in rice in Bhutan include a systematic assessment of crop yield losses; prioritization of weed importance and species shifts; mechanical and cultural alternatives to hand weeding; herbicide resistance testing and management; collective community approaches to area-wide management; and weed management options to suit alternative rice production systems. The ecology and management of the perennial semi-aquatic Potamogeton distinctus needs serious attention owing to its prevalence in major rice areas and potential alone to cause significant yield losses of up to 37%. The successful experiences and challenges in neighbouring Asian countries should also help to guide future weed control research in Bhutan.