Larvae to help rid lake of weed

The New Indian Express

5th June 2013

By Merlin Francis

Since September 2012, members of Puttenahalli Neighbourhood Lake Improvement Trust have been at war with a strange enemy - the salvinia molesta. This free-floating water plant rapidly multiplies to form a blanket over the lake, shuts out sunlight, blocks oxygen from the water, kills fish and denies birds around the lake any food.

But the battle took a decisive turn on Monday evening, with volunteers deploying a 2 mm soldier into the lake - the salvinia weevil sourced from the Kerala Agricultural University in Trichur. The weevil larva eats through the buds of the molesta, while the adults feed on its leaves.

The solution to this problem did not come easy for the volunteers of PNLIT, who, since they first identified the weed, have been manually removing it from the lake beds. “At least on three occasions since January, we roped in volunteers to remove the salvinia molesta. We thought we got rid of the salvinia, only to a find that a little bit was left behind and was now rapidly spreading through the lake a couple of days later,” recalled Usha Rajagopalan, founder trustee of PLNIT.

“Initially, the only solution we could find was to manually remove the weed. But, we got a lead from the Indian Institute of Horticulture Research, Bangalore, who in turn, put us in touch with Dr K R Laila from Kerala Agricultural University. An email was sent out to volunteers travelling from Thrissur to Bangalore to pick up a small box of the weevils. In a few hours, we received a response and the weevils arrived last week. On Monday, we released it near areas where the salvinia molesta were thriving,” she said and added: “The weevils may take anything between eight months and a year for visible effect on the weed.”

The salvinia molesta is a decorative plant used in aquariums which explains how the plant got to the lake, Rajagopalan said. “It is commonly used as a bio-fuel, although it was not an option that the PNLIT looked at,” he added.

While the salvinia thrives where water is polluted, the fact remains that as long as the water is being polluted with sewage, it will return to the lake.

Herein begins the trust’s other major concern - an encroachment of over one acre on the lake bed by slum-dwellers. The PLNIT has tried various methods to bring awareness among the slum-dwellers and to keep it clean. “We have done everything from drives to providing facilities on the lake bed for children, organised classes and helped them with studies. But, pollution into the lake continues,” she lamented. “Incidentally, the land has been allotted for the slum-dwellers at Bettadaspura and correspondence between the tahsildar and the DC has confirmed the handing over of the land in 2009,” said Rajagopalan.

Meanwhile, the pre-monsoon showers, along with the diversion channels put up from Brigade Millenium has filled almost 75 per cent of the lake area. “We have never seen the lake this full. Not since 2006, when we began work on the lake or after 2009, when we signed an MoU with the BBMP,” she pointed out. “Till now, water was being wasted. But with it being diverted into the lake, it is flourishing. People do not have to put up with flooded roads. Despite a lot of frustration, seeing our lake this year is keeping us motivated to continue the work,” she concluded.


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