Experiments were conducted to examine the biological effects of Kava, a perennial pepper plant native to oceanic region on paddy weeds and fungi harmful to plants and crops. Kava showed a strong inhibition on growth of barnyardgrass (Echinochloa crus-galli), monochoria (Monochoria vaginalis), and knotgrass (Paspalum distichum L.), which are among the most harmful paddy weeds. Kava completely controlled emergence of monochoria and barnyardgrass at a treated dose of 0.5 and 1.0g, respectively. Application of Kava at 1 tonne ha(-1) 6d after saturating paddy soil with water was an effective treatment. This caused around 80% reduction of natural paddy weed growth and increased tillering and root number of rice. In addition, Kava significantly inhibited growth of the five fungi: Fusarium solani, Pyricularia grisea, Rhizopus stolonifer, Taphrina deformans, and Thanatephorus cucumeris. The effect on R. stolonifer was the greatest and T cucumeris and P. grisea were the second most affected. The inhibition of Kava on paddy weeds was species dependent, proportional to the treated doses and inversely proportional to the time after watering. Kava is a promising material, which might be used as natural herbicide and fungicide in the field to reduce the dependence on synthetic herbicide and fungicide in agricultural production. (C) 2003 Elsevier Science Ltd. All rights reserved.