Use of azolla to suppress weeds in transplanted rice∗

Three fields with different weed floras were selected for the study. Weed species suppressed by azolla (Azolla pinnata R.Br.) were Monochoria vaginalis (Burm.f.) Presl., Echinochloa glabrescens Munro ex Hook.f., Cyperus difformis L. and Paspalum sp. The effect of azolla was assessed at two different stages of crop growth. At rice flowering the weeds were suppressed by 69–100%, and at harvest by 86–95%, depending on the weed species. Azolla failed to suppress the growth of Scirpus maritimus L. and Echinochloa crus‐galli ssp. hispidula (Retz.) Honda. When weeds were adequately controlled by azolla, yields from azolla‐treated plots were comparable with those from the hand‐weeded plots, and significantly higher than that from the non‐weeded control. When azolla failed to suppress the weeds, the yields from the azolla‐treated plots were similar to those from the non‐weeded control and significantly less than that from the hand‐weeded control.