Survey of Weed Management Practices in Direct-Seeded Rice in North-West Cambodia.

Two-hundred rice farming households from eight lowland rice villages in North-West Cambodia were surveyed in 2020 to determine changes in farmers' knowledge, weed management practices and weed seed contamination in seed kept for sowing. The major yield constraints cited by farmers were lack of water, inability to manage water and competition by weeds. Water shortages result in reduced crop establishment, non-optimal herbicide application timing and poor weed control. Reduced tillage, drill planting and use of pre-emergence herbicides can improve weed management. The adoption of drill planting improves crop establishment and enables the use of pre-emergence herbicides. Possible reasons for changes in weed problems include the change to a two-crop rice system in the wet season and spread of seeds by harvesting machines. The main weed seed contaminants of rice seed kept for sowing were Echinochloa crus-galli, E. colona, Fimbristylis miliacea, Ischaemum rugosum and Melochia corchorifolia. F. miliacea was the only species effectively removed by village cleaning methods. Although prevalent in rice fields, Cyperus. iria with <0.2 seeds per 500 g and Leptochloa chinensis with nil contamination were insignificant contaminants of seed samples. The majority of farmers in the study area are relying on repeated use of a narrow range of post-emergence herbicides, thus leading to increased severity of weed problems in dry direct-seeded rice. Integrated weed management is required to reduce over-reliance on post-emergence herbicides. This will require engagement with the local input supply network to introduce advice on improved weed management and sustainable herbicide use. [ABSTRACT FROM AUTHOR]