Weed competition in rice production.
Work on the distribution and competitive effect of rice weeds in Peninsular Malaysia is reviewed. At least 72 species have been identified in 209 311 ha of rice in the region. Major weeds of transplanted rice are Monochoria vaginalis, Limnocharis flava, Salvinia molesta, Fimbristylis miliacea and Scirpus grossus. In direct-sown rice (34-45% of the rice in the region), Echinochloa crus-galli, E. colonum, Leptochloa chinensis and Ischaemum rugosum are persistent. Weed competition is more severe in direct-sown than in transplanted rice (estimated yield losses 4 and 33%, resp.). E. crus-galli alone reduces the number of tillers, panicles and spikelets/panicle and can reduce yields by 41%, compared with losses from sedges and broadleaved weeds (10 and 28%, resp.). A min. 40-45-day weed-free period is required to ensure optimum yields. Tall cultivars such as Seberang, MR 79 and Makmur (height 89-93 cm) competed better with weeds (yield reductions of 22, 27 and 34%, resp.), than cv. Y960, Y963 and IR42 (height 62-72 cm) which suffered severe yield reductions. Studies on transplanted rice showed that S. molesta caused 12.5% yield reduction due to reduction in panicle-bearing tillers. The merits of integrated control for rice weeds in Malaysia are discussed.