Abstract:Malachium aquaticum (L.)Fries is a worst weed in rape fields. The emergence and population dynamics of M.aquaticum in transplanted rape fields was studied by survey of permanent quadrats and random quadrats, and field trials for herbicide screening were further conducted to develop the control strategy. The results showed that M.aquaticum reached the peak of emergence 3 weeks after rape transplanted, and the instant seedling amount was 117.0 plant/m2, accounted for 21.71% of its total seedling number (539.0 plant/m2). In mid December, the population of M.aquaticum reached the highest density of 407.8 plant/m2 and the cumulative emergence number was 82.19% of its total. This period was the critical time for control of M.aquaticum.Both foliage applied herbicides benazolin-ethyl and soil applied herbicides isoproturon had good control effects on M.aquaticum, the efficacy maintained over 95% 60 days after treatment and they had no side effects on the plant height, pod number and oilseed yield.