Summary:Experiment conducted in the glasshouse with water hyacinth plants in pots revealed that 3h.after spraying parquet or 2.4‐D at recommendeb herbicida rates, 43 to 53, of the herbicide is found in the plants and the rest is present in the water culture Out of the total [14Clparaquat applied,38,9,8·8. 32 and 0.9% was found in the leaf blads. petioles, underwater foliage and roots respectively. The corresponding values for [14C]2, 4‐D were 320. 94. 13 and 0.2% As the time interval after spraying increased, a greater accumulation of herbicide in the under‐water parts was evident A net loss of 14 and 60%. of the applied 2,4‐D was recorded 1 and 2 weeks after spraying respectively the rate of paraquat loss from the plant water system was similar to 2,4‐D.Absorption of [14C]2,4‐D from the culture solution by the roots and the floats of the water hyacinth was. evident Translocation of root‐absorbed 2, 4‐D into the meristematic folrar parts was dernonstrated If the substrates was treated with 2,4‐D.a minimal concentration of 1 p. p. m. was required for water hyacinth death In another experiment glyphosite at 2 to 6 kg a 1 ha and 2.4‐D.amine at 0–75 2.25 kg a ha gave complete control of water hyacinth Asulam was found to be unsatis factory even at 6 kg a.1 ha