Abstract
This study was conducted to determine a time for mechanical weed control and the effect of weed control by the cultivating weeder (C.W.) in rice paddy fields. Control efficacy by C.W. was from 50.7 to 64.6% at the one time application and 76.3% at the two times of 20 and 40 days after transplanting (DAT). The combination application of butachlor 5% GR and C.W. effectively controlled weeds by 91.8%. Rice yield was decreased at one time application of C.W. at 30 and 40 DAT but that in two times application of C.W. and butachlor 5% GR fb. C.M. plots were not significantly different with pyrazosulfuron-ethyl․mefenacet 3.57% GR plot. Annual weeds were increased with successive usage of C.W. for 2 years. Accordingly, weed control effect and yields in these plots were decreased. The cost of weed control using the C.W. was 1.2 to 2.3 times higher than that of herbicides plots