Abstract:In order to understand the effect of eclipta, Eclipta prostrata on rice growth and yield, and to provide effective economic parameters for the control of E.prostrata, a field experiment was carried out to study the change of light penetration rate, rice height and yield properties with different densities of E.prostrata by the methods of additive series experiment and curve fits. The results showed that while the density of E.prostrata≥2 plant/m2, the light penetration rate was reduced significantly. The significant decrease of the effective ear number, ear length and ear grain number and the significant increase of blighted grain number lead to the remarkable decline of rice yield associated with the increasing density of E.prostrata. The quadratic model (y=-0.0189x2+2.3546x+2.0819) could well fit the relation between the rice yield loss and the weed density. The economic infestation level for the E.prostrata by manual weeding was 22.22%, and its related economic threshold were 9.3 plant/m2, while for the chemical herbicides of 10% bensulfuron-methyl WP, the economic infestation level and related economic threshold were 4.67% and 1.1 plant/m2, respectively.