Weed research issues, challenges, and opportunities in Bhutan

Rice, maize and wheat account for 96% of the total food grain production in Bhutan signifying their importance for food security and the socioeconomic value of the Bhutanese agriculture. However, various biotic and abiotic factors impede optimum production of these cereals with weeds as one the main biotic constraints in attaining the full realisation of potential yields. In Bhutan, weeds have the potential to cause rice yield loss up to 50%. Similarly, 50% of the labour in maize production is for hand weeding. Key challenges for weeds management are labour availability, small farm sizes and potential risks of developing herbicide resistance from unsuitable usage patterns. Currently, rice is the only crop which receives herbicide, with long-term usage of a single chemical, butachlor. Manual weeding continues to be the main form of weed management in rice and maize, though the effectiveness of herbicide in maize has been demonstrated. Wheat is currently un-weeded, and no chemicals are used. Developing alternative herbicides to butachlor with different modes of action, and providing training on proper usage are likely to become more important. Considering the existing wide-spread use of low-external-input farming systems in Bhutan, non-chemical tactics will continue to have a key role in weed management. Some of these methods include competitive cultivars, optimum planting configurations, intercropping and strategic agronomic management. Incorporating these into an integrated package that includes herbicides may have long-term benefits for farmers. (C) 2017 Elsevier Ltd. All rights reserved.