Variation of Weed Occurrence and Rice Yield by Using the Cultivating Weeder for Three Years in Paddy Rice

This study was conducted to determine a appropriate time for mechanical weed control and the weeders effect by the cultivating weeder (C.W.) at different transplanting in rice paddy fields. Control efficacy by C.W. was from 82.3 to 82.5% by the one time application (15 or 30DAT), and 87.1% by the two times of 15 fb 30 days after transplanting (DAT) under one crop system in 2004. However, when grew continuously during 2∼3 years under usage of C.W., control efficacy by C.W. was 66.0∼72.7% by the one time application and 59.0∼69.4% by the two times, respectively. On the other hand, control efficacy by C.W. was 83.6∼85.7% at the one time application on 10, 15, 20DAT, respectively, and 90.7∼91.4% at the two times of 10 fb 20 days and 10 fb 30 DAT in two crop system (2005). The control efficacy the second year was 23.7∼56.3% which had been similar with one crop system for 3 years. The cost of weed control by C.W. was 1.2 times higher than that of herbicides at 10 fb 20 DAT, but economical effect was higher 11% than that of herbicides treatment.