Potential biological control of weeds in rice fields by allelopathy of dwarf lilyturf plants

Dwarf lilyturf (Ophiopogon japonicus Ker-Gawl), a medicinal plant, has been used for sore throat therapy and inhibition of physiological thirst since ancient times. Experimental studies were conducted to determine the allelopathic effects of dwarf lilyturf plants on germination and growth of three main weed species, viz., barnyardgrass (Echinochloa crusgalli L.), monchoria (Monocharia vaginalis P.) and smallflower umbrella (Cyperus difformis L.), in rice production and on emergence and growth of weeds in rice fields in Japan. These results showed that all aqueous extracts (1, 2, 4, 8%, w/v) from the dried powders of underground parts of dwarf lilyturf contained water-soluble substances that significantly inhibited seed germination and seedling growth for monchoria and smallflower umbrella. With respect to barnyardgrass, all aqueous extracts had less effect on germination, but low concentrations (< 2%, w/v) had stimulatory effects on growth. However, higher concentrations (> 4%, w/v) had significant inhibitory effects. In a glasshouse experiment, all treatments (50, 100, 150 g m(-2)) of the dried powders significantly inhibited the emergence and dry weights of weeds in rice paddy fields and the inhibition became stronger as the concentration increased, except that 50 g m(-2) concentration had slight stimulatory effects on the emergence of barnyardgrass. The 150 g m(-2) concentration markedly inhibited emergence (77.6%) and dry weight (91.1%) of rice field weeds. In addition, all treatments had no inhibition on initial rice plant growth. Dwarf lilyturf plants may have inhibitory potential on weeds as a natural rice field herbicide.