Developing weed management for direct-seeded rice systems in the Lao PDR

Lowland, small-holder farmers in the Lao PDR are moving from wet-season, transplanted rice (Oryza sativa L.) to direct-seeded rice (DSR) to save labour and time, and to respond to risks due to climate change. However, there is considerable evidence in South East Asia that when farmers transition to DSR, weeds are a major constraint to adoption. DSR is in the early stages of development in Laos and farmers urgently need information on best management practices to reduce impacts of weeds on rice yield and weed seedbanks. In August/September 2018 during the wet season, we combined field observations and a questionnaire of farmers to determine the most common weed species, densities and farmers’ current weed control practices in DSR systems in Savannakhet Province of the Lao PDR. The study found that farmers’ understanding of the impact of weeds on rice yields is limited. The most prevalent weeds were sedges, Fimbristylis miliacea, Cyperusiria, C. difformis and C. rotundus, and grasses, Echinochloa ssp. and Leptochloa chinensis. Weed densities of more than 50 plants/m2were observed prior to hand-weeding in 21 of the 35 fields (60%). We found that 83% of farmers use hand-weeding, 11% do nothing, and 6% use some herbicide. The study identified a significant need for supporting farmers and advisors in developing tools for: a) weed management, and b) weed recognition. In 2019, we began a program to examine integrated weed management techniques in DSR with small-holder farmers and their advisors. Te c h n i q u e s i n v e s t i g a t e d i n c l u d e : p l a c e m e n t o f f e r t i l i z e r a t s o w i n g c o m p a r e d t o b r o a d c a s t 1 4 days after sowing, to increase rice emergence and vigor; early interrow cultivation; crop/weed cutting and removal before weed seed set; and late-season, needs-based hand-weeding, to prevent weed-seed set. This is a collaboration between the Crawford Fund of Australia, the Australian Volunteers Program and the Provincial Agriculture and Forestry Office of Savannakhet. The long-term aims are to observe changes in weed spectrum over time, build the capacity of farmers and advisors to control weeds in DSR, to reduce weed seedbanks, and to maximize profits and environmental outcomes.