A wedge shaped growth of salvinia

Mats of the aquatic fern, Salvinia molesta, can clog waterways causing disruption to their use.

Biological control of the aquatic weed, Salvinia molesta

Infestations of the aquatic weed, salvinia, disrupted waterways in tropical countries but biological control using a tiny weevil brought it under control in many places.

  • 24 June 2009 | Updated 5 December 2011

About salvinia

First recorded in Australia in 1952 and originating in south-eastern Brazil, the aquatic fern Salvinia molesta became a serious aquatic weed in Australia, South-East Asia, the Pacific and south, central and eastern Africa.

View the classic short documentary from 1985 'Assault on the Sepik' about Salvinia management in Papua New Guinea.

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Assault on the Sepik
1985 film documenting the CSIRO-led effort to combat the water weed Salvinia molesta using biological control methods.

In Australia it spread over a vast area - from the Northern Territory and Cooktown in North Queensland,  down the east coast to Melbourne Victoria in the south, and across to Western Australia.

Salvinia grows quickly to form thick mats covering lakes, slow-moving rivers and other waterways. These mats severely interfere with the use of water bodies for boating, irrigation, flood mitigation and conservation of wildlife. Once vital waterways become stagnant ponds supporting only salvinia. In some countries village life is disrupted because waterways are no longer navigable.

The tiny weevil, Cyrtobagous salviniae, has controlled salvinia in many countries.

Salvinia has a phenomenal growth rate, doubling its dry weight in two and a half days when conditions are right.

Biological control

In 1978, CSIRO scientists began the search for biological control agents in southeast Brazil which they had identified as the native range of salvinia. They found three promising potential agents:

  • a weevil (Cyrtobagous salviniae)
  • a moth (Samea multiplicalis)
  • a grasshopper (Paulinia acuminata).

C. salviniae was the first to go through the formalities required before an agent can be released in Australia. In 1980, the first releases were made on Lake Moondarra, an artificial lake providing water and recreation for Mt Isa in north Queensland, which was heavily infested with salvinia. By mid-1981, the beetle had reduced the salvinia to a few small patches.

Surface of Lake Moondara almost completely covered due to an infestation of Salvinia Salvinia molesta.

Lake Moondara in Queensland, Australia infested with the weed Salvinia, Salvinia molesta.

Surface of Lake Moondara completely free of Salvinia after the introduction of a biocontrol agent.

Lake Moondara in Queensland, Australia after the introduction of a salvinia biocontrol agent.

This one, 2 mm long weevil went on to clear massive infestations of salvinia in areas like the Sepik River (Papua New Guinea), Sri Lanka, Wappa Dam and Lake Moondara (Queensland, Australia) and lagoons in the Northern Territory, Australia, including in Kakadu National Park. In all, salvinia has been controlled by C. salviniae in at least 13 tropical countries.

The CSIRO team that unravelled the complex story of salvinia and Cyrtobagous taxonomy and instigated the biological control project received the UNESCO Science Prize in 1985 for their work in PNG.

The moth, S. multiplicalis, also released in Australia, established and spread but was ineffective. It was decided not to release P. acuminata.

Learn more about the Ecology and management of Australian weeds.