Aquatic weeds problems and management in India

Aquatic weeds are those unwanted vegetation which grow in water and hamper its use. Out of about 160 aquatic weeds, Eichhornia crrassipes, Ipomoea aquatica, Typha angustata, Ceratophyllum demersum, Salvinia molesta, Nelumbo nucifera, Alternanthera philoxeroides, Hydrilla verticillata, Vallisneria spiralis, Chara spp., Nitelia spp., Potamogeton spp. are of primary concern in India. Several irrigation and hydroelectric projects in the country like Nagarjuna Sagar project in Andhra Pradesh, Tungabhadra project in Karnataka and Kakki and Idikki reservoirs in Kerala are suffering with massive growth of aquatic weeds. Weeds enhance rates of evaporation many folds through evapotranspiration than that of open surface, thus cause great loss of water. Water hyacinth makes water unfit due to eutrophication and slows down the flow rate of water besides causing many health associated problems. Aquatic weeds can be controlled by several methods like biological, chemical and physical. Each method has its benefits and drawbacks. There are several popular control mechanisms for preventing the spread or eradication of aquatic weeds. Physical methods are suitable only for small scale infestation but when applied in large water bodies become ineffective due to high cost and regrowth. Chemical control has been practiced against aquatic weeds since long time in India but it is not prevalent. Control of small infestations with herbicides has often been very effective, but is heavily dependent on skilled operators who maintain longterm vigilance for appearance of regrowth or seedlings. In recent decades, there has been a significant increase in the level of nutrients dumped into water from industrial and domestic sources as well as from land where fertilizers are used or where clearance has caused an increase in run-off. Successful attempts have been made to control water hyacinth and water fern by use of exotic weevil Neochetina spp. and Cyrtobagaus salvinae in different parts India but for several other aquatic weeds, suitable bioagents are not available. Some species of herbivorous fishes (Tilapia spp. and Ctenopharyndon idella) have been utilized to control some submerged weed especially Hydrilla spp. with varying degree of success. This paper describes the aquatic weed problems in India and the efforts made so far for their management by various methods.