Weed watchers unite in Malaysia and Sri Lanka

Malaysia and Sri Lanka have many things in common. In both countries, labor costs are relatively high, rice is largely established by direct seeding, and weeds cause major problems, especially weedy rice.
Weedy rice is closely related to cultivated rice and is a serious threat in direct-seeded rice. At present, no single management technique can effectively control weedy rice.

Malaysia, Vietnam, and Thailand have the largest areas in Asia in weedy rice infestation. “When the weed first appeared in Malaysia in 1988, farmers did not recognize it as a problem and did little to check its spread,” says Dr. Azmi bin Man, weed scientist and collaborator of the Irrigated Rice Research Consortium (IRRC) Labor Productivity Work Group (LPWG). “Now, most rice fields in Peninsular Malaysia and Sabah are affected, and it is estimated that weedy rice is causing crop losses valued at US$25 million a year on the peninsula.”

Experiments have been done in Malaysia through collaboration with Dr. Azmi and the Malaysian Agricultural Research and Development Institute. Main efforts are aimed at identifying the amount of yield losses and determining the influence of establishment measures. Awareness of the problem has been raised through the production of the Be aware of weedy rice in Asia brochure, which has been translated into four languages. Making people aware of weedy rice is an important step, as initial infestations can be overlooked, allowing the problem to become worse. If farmers are aware of weedy rice, they can check their seed supplies and control the spread.

Yield losses due to weeds in irrigated rice in Asia are thought to be about 10%, but may be higher in areas where weeds survive early control measures, particularly in direct-seeded rice. Changes in crop establishment methods result in shifts in weed species, and farmers may have to adapt their management practices accordingly.

Meanwhile, Dr. Anuru Abeysekera, a scientist with the Rice Research and Development Institute (RRDI) at Batalegoda, reports that the rice areas in Sri Lanka are either rainfed or are only partially irrigated, and more than 90% of farmers practice direct seeding. Crop management is variable and farmers use different direct-seeding practices to account for differences in the availability of water, soil type, and resources.

Dr. Abeysekera has been conducting field experiments in 2005-07 with the LPWG at the RRDI and comparing five crop establishment methods to select the best practices that can be adapted in specific rice environments to reduce yield losses due to weeds. The different establishment methods being tested are broadcast wet seeding, row seeding using a drum seeder, water seeding, zero tillage, and seedling broadcasting.

Results show that row seeding is an effective establishment method in the rice fields at RRDI as it is easier to do follow-up hand weeding. Researchers are also studying the longevity of seed viability of weedy rice (Oryza sativa) seeds collected from different areas in Sri Lanka. These seed bank studies will continue until April 2009. The change from transplanting to broadcasting has resulted in a dramatic succession of weed species from ones that are relatively easy to control to others that are difficult to manage. Weedy rice is one example of such a change. Recently, in Ampara and Puttalam districts, many farmers complained that they could not cultivate their fields because of weedy rice, and yield losses were estimated at 30–100%. It was for this reason that the studies on the impact and control of weedy rice in Sri Lanka are a priority.

Training activities were also conducted by extension officers and farmers on weedy rice, crop establishment by direct seeding in the different rice environments, and the use of the drum seeder. More demonstrations for farmers will be conducted on using a drum seeder, water seeding, and zero-tillage techniques in 2008.

David Johnson (d.johnson@cgiar.org) and Trina Mendoza (t.mendoza@cgiar.org)

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