Abstract: The replacement of the senescent lotus population is a problem in our seed-lotusproduction at present.Through experimental extermination of the undesirable popu-lation with herbicides,we have solved this problem basically.Lotus plant is fairly susceptible to herbicides of the phenyloxy-acetic acid group.A dosage of 75—125 g of the emulsifiable oil of 72% butyl 2,4—dichlorophenyloxy-acetate per mu (=1/15 hectare),applied to leaves and stalks with an atomizer,issufficient to bring about a through-going eradication of the population,includingthe underground rhizomes as well as the leafy shoots.Yet such treatment seems toleave no ill effect on fish and its food organisms.Season appropriate for applyingherbicide begins from the time when the plant develops to the stage of luxuriantvegetative growth,and ends at the stage of full blossom (prior to the formation ofnew rhizomes).The method is especially suitable for those farms which are short of man-powerbut where the area of senescent population (or of wild lotus) to be treated isextensive.