Biology and Control of Perennial Paddy Weeds

Abstract

Control of perennial weeds, which have recently begun to grow rampantly in the paddy fields, is creating a new problem in rice cultivation in Japan. The present paper intends to give information on the kinds of perennial weeds grown in paddy fields and their distribution, and to review the ecological characters of the major weeds in Japan and the control measures by herbicides. Those presently causing trouble are Scirpus hotarui OHWI, Alisma canaliculatum A. BR. et BOUCHE, Sagittaria trifolia L., Sagittaria pygmaea MIQ., Cyperus serotinus ROTTB. and Eleocharis kuroguwai OHWI. Among them, S. hotarui and A. canaliculatum propagating themselves mainly by seeds, are dominant in North Japan, and others which use tubers for propagation, are widely distributed from the eastern part to western districts of Japan. Generally speaking, perennial weeds root deep, and dormancy period of seeds or tubers which rest, is not consistent. Moreover, they grow and decay very slowly. These characteristics do not allow herbicides to bring about a satisfactory result; consequently, the integral control through proper combination of herbicides becomes necessary. Presently emphasis is put on the development and utilization of mixed compounds which are capable of controling both annual and perennial weeds simultaneously.