A short review of the impact and management of weedy rice
S.M. Rezaul KarimA, B.S. IsmailB and M. AzmiC
A Department of Agronomy, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.
B School of Environmental and Natural Resource Sciences, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia.
C Food and Industrial Crop Research Centre, MARDI Seberang Perai, PO Box 203, 13200 Kepala Batas, Penang, Malaysia.
Weedy rice consists of the early shattering biotypes of cultivated rice (Oryza sativa L.) and the natural hybrids of Oryza spp. and the cultivated rice varieties. Some important characteristics of weedy rice include comparatively early maturation, easy shattering, short shattering periods, red pericarp (in some strains), short grain, long awns and tall plant habit. Continuous direct seeding over the seasons and poor water management are the main factors enhancing infestation with weedy rice biotypes. Under moderate infestation (15-20 panicles m-2) there occurs about 50-60% yield loss and with high infestations (20-30 panicles m-2) up to 70-80% yield loss. Weedy rice seeds are an important contaminant of rice seeds, as they diminish farmers' income qualitatively and quantitatively. On an average there is 17-28% indirect cost through land preparation and 3-5% direct cost through manual weeding or roguing, incurred for controlling the weed. The farmers may get a return of US$105-374 ha-1 if the weed is controlled properly. An integrated approach including the use of clean certified seeds, sequential tillage for land preparation, burning of rice straw on the field, spraying of herbicides as a pre-planting procedure, manual weeding at the mid stage of rice growth and the use of transgenic herbicide-resistant rice cultivars, are suggested options to control weedy rice populations. The practice of water seeding and transplanting of rice seedlings instead of dry seeding and the rotation of rice crop with other upland crops like soybean and maize are recommended practices to effectively manage the weedy rice problem.
Plant Protection Quarterly (2006) 21 (1) 13-19.