Abstract: Crabgrass (Digitaria sanguinalis), goosegrass (Eleusine indica), redroot pigweed (Amaranthus retroflexus) are the three dominant weed species in summer maize fields. To get more scientific weed control strategies, we adapted the De Wit replacement series design to examine the competitive effects of mung bean on the three weed species under different mixed ratios. Results showed that plant height and biomass of crabgrass, goosegrass, and pigweed decreased with increasing mixed ratios of mung bean and weeds. Compared with the monoculture, plant height of crabgrass, goosegrass and pigweed decreased by 19.4%, 17.9%, and 14.7%, and dry weight decreased by 71.7%, 78.0%, and 38.2%, respectively, when the ratio was 3∶1. Under mixtures, the number of tillers of crabgrass and goosegrass was significantly reduced under different mixed ratios. However, side shoot number of pigweed decreased significantly only at the mix ratio of 3∶1 (P<0.05). Under different mixed ratios, the relative biomass of crabgrass, goosegrass and pigweed was lower than 1.0 (P<0.05). Relative biomass of weeds decreased with the increasing mixed ratio of mung bean. Our results indicated that mung bean was strong competitive to the three dominant weeds, and the competitive ability increased with its density. Competitive balance index between mung bean and crabgrass or goosegrass was significantly greater than 0 (P<0.05), but that between mung bean and pigweed was significantly greater than 0 only at the higher mixed ratio (3∶1) (P<0.05), indicating that competitive ability of mung bean to the grass weeds was greater than the broadleaved weeds.

Key words: Vigna radiata, weed, competitive effect, competitive balance index.