Weed research issues, challenges, and opportunities in Cambodia

The area of cultivated agricultural land in Cambodia is 3.7 million hectares with 76% of this planted to lowland rice and 24% planted to upland crops such as cassava, maize, soybean, sugar cane and vegetables. Cambodia's average rice paddy yield at around 3 t ha(-1) is around 50% of the yield potential and losses caused by weed competition have been shown to be a significant constraint. The most important issues currently affecting weed management in Cambodia's cropping systems are (a) increased climate variability and climate change, and (b) migration of labour from the rural workforce and consequent rapid mechanisation of agriculture. As a result of climate change, the wet season in Cambodia now begins and ends approximately one month later, and the bimodal rainfall distribution has strengthened, resulting in more extreme events of drought and flood during the wet season. A decline in the availability of agricultural labour has resulted in rapid mechanisation of land preparation, broadcast seeding, herbicide use and machine harvesting of rice and these changes have had significant repercussions for weed management. The resultant challenges and opportunities for weed management are presented and discussed. The main weed management challenges are associated with rice crop intensification, transition from transplanting to direct-seeded rice, changed planting dates and tillage practices in response to climate change, over-reliance on post-emergence herbicides, excessive inversion tillage, and lack of knowledge about the safe and efficacious use of herbicides. Opportunities for improved weed management in Cambodia's cropping systems include the development of integrated weed management for double crop intensive rice systems, transition from hand broadcasting to drill-seeded rice, new seeding windows and minimum tillage, non-transgenic herbicide resistant crops and education and training of input sellers and farmers to improve safety and efficacy of herbicide use. (C) 2017 Elsevier Ltd. All rights reserved.