Of a number of herbicides used in Pistia clearance, as a control measure of rural filariasis (Wuchereria malayi) in Ceylon, Phenoxylene 30 (MCPA) and 2,4-D amine salt were found to be the most effective, cheapest, and easiest to handle. 56 ml (2 fluid ounces) of Phenoxylene 30, and 28 ml (1 fluid