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Environmental weeds

Our new environmental weeds booklet aims to help residents identify weeds and provide information about appropriate weed control methods.

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Salvinia (Salvinia molesta) is an introduced fern from South America that is a declared noxious plant for the whole of Australia. It is a State-declared Category 3 pest plant species, and has a Weeds of National Significance (WONS) status which means the species is already spread over substantial areas of Queensland, but its impact is so serious that it requires active control to avoid further spread onto properties that are still free of the pest (Department of Employment, Economic Development and Innovation, 2011).

It can rapidly double in size within one week under optimal growth conditions and forms mats that completely cover lake systems, affecting water quality, flow, wildlife and recreational activities (i.e. fishing). It is a free-floating aquatic fern with small, spongy, green leaves positioned in pairs along a common stem. The species can be confused with the native Azolla species.

Department of Employment, Economic Development and Innovation 2001, Declared plants of Queensland, The State of Queensland.

Sainty G.R. and. Jacobs S.W.L., 2003. Waterplants in Australia. Sainty and Associates Pty Ltd, Australia.

Department of Primary Industries and Fisheries 2007, Fact sheet invasive plants and animals Salvinia, Biosecurity Queensland, State of Queensland.

City of Gold Coast integrated management program for this pest plant involves mechanical removal, application of registered herbicides and the introduction of biological control agents.


The Salvinia weevil (Cyrtobagous salviniae) was discovered by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in 1979. The weevil originates from the same native range in Brazil as Salvinia. Extensive host specificity testing was completed to ensure the weevil was not going to affect non-target species. The adult weevils feed on the Salvinia plant. However, most damage is done by the larvae tunnelling into the plant’s stem (rhizome). This causes the plant to turn brown, lose buoyancy and sink.

As part of an integrated approach, the City monitors weevil infestation levels and will implement mechanical removal if Salvinia is growing too fast. Removal of damaged Salvinia is implemented before it decomposes and negatively affects water quality.


For further information regarding management of this species, click on the link below or alternatively, contact us on 1300 GOLD COAST or 07 5582 8211.

Find answers to frequently asked questions about Salvinia below.

Related information

Jump to key information
  • Is it Salvinia?

    Salvinia is an aquatic fern that floats on top of the water. Salvinia is a declared pest plant which means landholders, including the City, must take steps to keep their land/water free of this plant. Salvinia originates from South America. In Australia it has no natural predators and flourishes in slow moving watercourses rich in nutrients. Salvinia can be confused with the native aquatic fern Red Azolla or mistaken for algae. Salvinia can be distinguished from red azolla and algae by the pairs of hairy floating leaves along the stems.

  • Where does it come from?

    Salvinia is found throughout the city with all catchments having this weed present. Moved by water and wind the plant can 'appear' overnight when there is a change in wind direction or a rain event. In optimum conditions salvinia can double in size every 5-7 days.

  • How does salvinia spread?

    In Australia, Salvinia does not normally produce seed, instead spread is from fragments of the original plant. Salvinia can be moved from one water body to another by people (deliberately or accidentally), wildlife and flooding.

  • What is the City of Gold Coast doing about it?

    To reduce the risk of re-infestation, the City is surveying water bodies in the upper catchment to identify Salvinia infestations and ensure effective control is implemented. We use an integrated management approach that includes establishing populations of a biological control agent called the Cyrtobagous salviniae (Salvinia weevil).

  • What is integrated management?

    Integrated management utilises the following methods collectively.            

    • Booms - restrict the movement of Salvinia, effective in ensuring Salvinia weevils establish viable populations quickly. High flow rates can damage booms.
    • Mechanical harvesting - suitable for removing floating mats of Salvinia in water deeper than 0.5 metres, very expensive and can amplify turbidity.
    • Physical removal - suitable for small ponds and lakes. The City supports SEQ Catchments Salvinia busters program.
    • Chemical - suitable for small infestations and mopping up Salvinia after mechanical or physical control.
    • Biological - suitable for waterways that are not shaded. Extremely economical and a long term solution, requires patience.
  • What are Salvinia weevils?

    Cyrtobagous salviniae (Salvinia weevils) are native to South America. Originally introduced into Australia in the 1970s, these biological control agents only complete their lifecycle on Salvinia. They do not eat any other plants.

  • How long do the weevils take to work?

    Weevils can control mats of Salvinia within a month, however regrowth of Salvinia can continue for up to three years. Once established, weevils need time to increase their population to a size where they are eating the Salvinia quicker than it can grow. As the Salvinia is eaten, their numbers decrease allowing Salvinia to regrow. This is then followed by an increase in the weevil numbers. This cycle will continue until the Salvinia and weevils reach an equilibrium.

  • How do the Salvinia weevils work?

    Adult Salvinia weevils will eat the leaves of the plant. The main damage is done by the weevils larvae as they tunnel through the plant destroying it’s buoyancy and allowing the plant to sink and decay.

  • Why has harvesting stopped?

    Harvesting only provides a temporary solution. The City has reduced harvesting due to success in establishing weevil populations. The City will implement harvesting to maintain navigation channels and if environmental conditions prevent establishment of large weevil populations.  

  • What is Salvinia sprayed with?

    City of Gold Coast uses a herbicide registered for the treatment of Salvinia by the Australian Pesticides and Veterinary Medicines Authority (APVMA). The herbicide is registered for use in waterways and does not affect fish, birds reptiles or frogs. Staff are trained and follow all safety instructions when applying herbicides.

  • Where can I get advice or assistance about Salvinia management?

    You can contact City of Gold Coast by telephone, email, online, post, fax or in person.


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