Herbicidal control of water hyacinth (Eichhornia crassipes) and its impact on aquatic environment

A research programme was taken up to study the impact of herbicides on the control of water hyacinth [Eichhornia crassipes (Mart.) Solms-laubach], optimize dose and time of application, and to trace the impact on aquatic environment through a series of greenhouse and pond studies. The study was undertaken at Veeranum Lake which has a command area of 18, 000 ha connected through 27 distributary channels, and infested heavily with water hyacinth. Among the different herbicides tried, viz. glyphosate, 2, 4-D Na salt and paraquat, glyphosate proved more efficient with higher magnitude of plant height reduction, weed mortality and reduction in biomass compared with 2, 4-D and paraquat. The optimum dose of glyphosate, 2, 4-D Na salt and paraquat was 2.5 kg/ha, 1.5 kg/ha and 1.5 kg/ha respectively. Different seasons did not influence the efficacy of herbicides. Glyphosate caused least fish mortality of 23.3% after 32 days. Different organs like gills, brain, liver and kidney of the fishes were studied, for histology and the observations showed tissue distractions in herbicides-treated fish. Glyphosate also proved more efficient and safe on water quality in terms of pH, electrical conductivity, dissolved oxygen, chemical oxygen demand and mineral content of treated water. The glyphosate-treated water was found safe for irrigating crops with 87, 58 and 62% germination of rice, cotton and okra respectively.