Aquatic Weeds in Sri Lanka

Darshani Samarakkody

Sri Lanka is an agricultural country with a population of 19 million people. Farmers and farming communities rely on a multitude of reservoirs for water as the country knows prolonged dry periods. There are some 50000 reservoirs in Sri Lanka ranging in size from 10Km2 to 1045 Km2, which have been constructed over the past 3000 years mainly for irrigati. The rural communities in Sri Lanka depend on inland water for rice and vegetable production, animal protein as well as fresh water supply. In recent years, moreover the country has seen a rapid increase in the number of dams, reservoirs and canals resulting from development of irrigation and hydroelectric projects. Recent observation and reports have demonstrated that both natural and artificial water bodies in Sri Lanka have become infected with the aquatic weeds.

In its native range water weeds is largely restricted to costal lowlands and along the margins of lagoons and slow moving waters. It occur low densities, only becoming a problem where the hydrological regime of a water body has been altered by human activities, or where the level of nutrients in the water has been increased. They provide a habitat for vectors of several diseases, increase the areas at risk as a result of flooding, and affect drinking water supply, inland fisheries and rural transport. The mosquito populations have increased at an alarming rate during the last five years due to the large mat of floating weed infestations in coastal districts.

Programms to control its growth have been initiated in most countries where it occurs. Chemical and mechanical control measures have been used to combat water weeds, but are expensive and ineffective on all but small infestation. Eradication of the weed has been rare because of its rapid growth rate and its ability to reinfest from seeds or isolated plants. Increasing concern about the financial and environmental costs associated with herbicidal control measures and their limited effectiveness has led to growing interested in the use of biological control. Biological control of water weeds offers sustainable, environmentally-friendly, long-term control and is the only feasible method to provide some level of control to those infestations which cover huge areas, are difficult to access and / or do not warrant the high cost of physical or chemical control.

The area colonized by this weeds appear to have increased in the recent years as the Government suffers from foreign exchange difficulties, lack of aquatic management knowledge, expertise and programms. Thus aquatic weeds have received very little attention in Sri Lanka so far.