IMPACT OF HERBICIDAL CONTROL OF WATER HYACINTH [EICHHORNIA CRASSIPES (MART.) SOLMS] ON AQUATIC WATER SHED S. Deivasigamani 1 * and R. M. Kathiresan 2 Department of Agronomy, Faculty of Agriculture, Annamalai University, Annamalai Nagar-608 002 (Tamil Nadu), India. Abstract Different herbicides viz., 2, 4-D Na salt @ 1.50 kg ha -1 , Glyphosate @ 2.50 kg per ha and Paraquat @ 1.50 kg ha -1 have been used to study the efficacy for controlling water hyacinth (Eichhornia crassipes), a potential aquatic weed on water shed. Among the treatments tested, application of glyphosate has shown maximum reduction of plant height, biomass at 50 DAS and chlorophyll content and increased the mortality of E.crassipes in stagnant water sheds. However, all the herbicides exerted 100 per cent mortality at 50 DAS. Key words : Eichhornia crassipes, herbicides, 2, 4-D Na salt, Glyphosate, Paraquat, stagnant water shed. Plant Archives Vol. 13 No.1, 2013 pp. 121-122 ISSN 0972-5210 Introduction The aquatic weed water hyacinth [ Eichhornia crassipes (Mart.) Solms-laubach] is considered to be the world’s worst aquatic weed (Julien et al., 1999). It belongs to the family pontederiaceae and is a native of tropical South America (Cronk and Fennessy, 2001). Water hyacinth is an erect, free-floating and one of the most troublesome weeds all over the world and is most damaging aquatic weeds of India. In India, the plant was first introduced in Bengal, most probably in early 1890s and has spread to all types of water sheds throughout the country (Haider, 1985). At present, it is believed to occupy over 0.2 M ha of water surface in India (Jayanth, 2000). According to Cronk and Fennesy (2001), leaves make up 60 to 70% of the plant biomass and the leaf turnover rate is high with about 60 to 70% of leaves being replaced each month, resulting in 60g of biomass accumulation per m 2 per day (Cook, 1993). Excessive infestation of the weed forms dense floating mats, which deleteriously affect water traffic, fishing potential, infrastructure for pumping, hydro electricity generation and biodiversity. Another potent consequence of water hyacinth infestation is heavy water loss due to evapotranspiration which is 1.02 to 9.8 times higher than evaporation from an open surface (Singh and Gill, 1996). Several mechanical, chemical and biological methods have been used to control water hyacinth. Frequent mechanical removal of this weed is highly expensive, laborious and time consuming process. Biological control require a minimum of several years, usually 3 to 5 years, for insect population to increase to density that could bring down the weed stand to a substantial decline (Harley et al., 1996). Based on the above facts, the study was conducted to screen herbicides for effective control of Eichhornia at early. Materials and Methods The water sheds trials were conducted at Annamalai University, Annamalai Nagar (Tamil Nadu), India, located at 11º24’ N Latitude, 79º44’ E Longitude and an altitude of +5.79 MSL. Stagnant water shed with a dimension of 70m × 10m with a water depth of 1.5m. The experiment was laid out in a randomized block design with three replications. The pond was divided into four compartments and each one is separated from the others using fish nets to prevent the movement of water hyacinth from one treatment to others. Three foliage applied herbicides tested were 2, 4-D Na salt @ 1.50 kg ha -1 , glyphosate @ 2.50 kg ha -1 and paraquat @ 1.50 kg ha -1 . The spray fluid of 500 l ha -1 has been applied using pedal sprayer fitted with flat fan nozzle. The plant height, biomass and mortality were recorded at 50 DAS whereas chlorophyll content was recorded at 7 days interval and upto 28 DAS. Chlorophyll content was estimated using spectrophotometer (Hiscox et al., 1979). Water hyacinth *Author of correspondence : E-mail : agrisiga2007@gmail.com