Water weed removed with surgical precision

Blog written by PT Bandara, CABI Associate, and WMDH Kulatunga, Sri Lanka.

Proliferation of Salvinia molesta in tank No.4 in March 2014.
Proliferation of Salvinia molesta in tank No.4 in March 2014. Images: Thushari Weerakoon, Moragahakanda Kaluganga Development Project.

“A looming threat imposed by Salvinia molesta was averted through the introduction of a biocontrol agent by technical experts of the Department of Agriculture.” These were the words of Project Director Engineer RB Tennakoon, of the Moragahakanda Kaluganga Development Project, Sri Lanka; a project with the key objective to improve the availability of irrigation to water-scarce farmlands and thereby increase crop production and productivity in the area surrounding Kaluganga and Moragahakanda reservoirs, as well as supplying domestic water to Anuradhapura, Trincomalee and Matale districts.

Salvinia molesta recently replaced Rinderpest virus on the list of “100 of the world’s worst invasive alien species” in a global survey conducted in 2013 where over 650 invasion biologists participated. It is a water fern which forms dense mats over water reservoirs and slow moving rivers, causing large economic losses and a wide range of ecological problems to the environment, native species and communities. It can clog water intakes and interfere with agricultural irrigation water supply and hydropower generation.

One of the water tanks at Kaluganga was completely covered with Salvinia in March 2014 and there was a huge possibility of spread of Salvinia throughout the irrigation system of Kaluganga Project. The case was referred to the Plant Protection Service of the Department of Agriculture. Within ten months the tank was clear of Salvinia, without the use of any mechanical tools or chemicals but using a control method perfectly compatible with nature. What made this possible?

It is due to a tiny weevil Cyrtobagous salviniae used as a biocontrol agent. Larvae of  C. salviniae tunnel within the rhizomes/stem causing them to disintegrate. Larvae also tunnel in the buds and adults eat buds, thus suppressing growth and vegetative propagation of this sterile weed. Technical experts from the Plant Protection Service of the DoA, who are responsible for rearing this weevil  provided a culture of the biocontrol agent and introduced them into the infested water bodies.

The elimination of this troublesome weed led to the jubilation of the Project Director. Mr Tennakoon acknowledged the support given by Mr PT Bandara, Deputy Director Plant Protection Service at the time of this project, and his team in removing this highly invasive water weed and thus eliminating a huge threat that would have jeopardized the Moragahakanda Kaluganga Project.

Find out more about management of this weed by searching “Salvinia molesta” on the Plantwise knowledge bank, including factsheets from the DoA, Sri Lanka in Sinhala and Tamil.

The case was referred to the Plant Protection Service. Mr WMPT Bandara and other technical experts visited the tank and released specific biological control agent on 14 March 2014.
The case was referred to the Plant Protection Service. Mr WMPT Bandara and other technical experts visited the tank and released specific biological control agent on 14 March 2014. Images: Thushari Weerakoon, Moragahakanda Kaluganga Development Project.
By June 2015 the tank becomes clear and the control method is a success
By June 2015 the tank becomes clear and the control method is a success. Images: Thushari Weerakoon, Moragahakanda Kaluganga Development Project.

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