Land for Wildlife member, Leanne Field, releasing Salvinia Weevils into a Salvinia infestation on her property.
Regarded as one of the worst weeds in Australia, Salvinia (Salvinia molesta) is a floating aquatic fern inhabiting still or slow moving water. Salvinia thrives in nutrient rich waters. This allows it to colonise most water bodies such as agriculture run-off, wastewater, wetlands and dams. Salvinia is a Class 2 Declared Pest under Queensland legislation and is also a Weed of National Significance (WONS). State Government legislation requires landholders to manage infestations on their properties. Salvinia was brought to Australia from Brazil in 1952 as an ornamental plant. Infestations soon exploded and almost all water bodies nearby were colonised by Salvinia; the introduction of this weed has been regretted ever since.
Salvinia has unusual features allowing this species to dominate and succeed. The leaves have tiny egg-beater shaped hairs that repel water and enable it to float. Each node has false leaves that are submerged and modified to act as a root. Morphological variation (variable size and shape) within the species is considerable and greatly depends on age, nutrient availability and the size of infestations.
Infestations in our waterways are a major hurdle for biodiversity, water quality and the aesthetic values of riparian areas. Salvinia dominates the surface of exposed water bodies, forming dense mats and altering ecosystem function by excluding light penetration, preventing the transfer of oxygen from the air and effectively decreasing dissolved oxygen levels.
Competing with native vegetation and preventing aquatic wildlife from finding refuge, food or nests, Salvinia plays an influential role in prohibiting the distribution of Australia’s native flora and fauna. In some regions, Salvinia also adversely affects pastoralism, tourism, recreation and traditional hunting practices. Hydrogeological regimes have also been altered by Salvinia infestations impeding the access of wildlife and stock to floodplains and water bodies.
Like many weeds, Salvinia has traits that make it highly invasive. It can be dispersed through various methods such as floodwaters, birds and other wildlife. It grows rapidly, has limited natural predators and out-competes native aquatic plants. Salvinia reproduces by forming new branches that break off and re-establish quickly. Salvinia still has fern-like traits where spores are contained in sporocarps attached to the roots, however they are either empty or contain sterile spores. This is an unusual feature for a fern!
Salvinia dies in salt water; therefore, floodwaters flushing Salvinia out to sea can play a key role in managing infestations. Preventing further spread outside of core infestations should be a main management objective. It is easier and more cost effective to prevent new infestations than to control an established infestation.
One effective method of Salvinia management is biocontrol using the Salvinia Weevil (Cyrtobagous salviniae). In 1980, the Salvinia Weevil was released by CSIRO into Lake Moondarra near Mount Isa. This lake had a Salvinia infestation that covered an estimated 800 hectares and weighed more than 50,000 tonnes. This was significantly reduced to just one tonne within one year. It is important to note that eradication of Salvinia will not be achieved with the sole use of biocontrol as a healthy amount of weed is always needed to sustain an ongoing population of weevils.
Weevils can live for about six months with a completed life cycle only taking six to eight weeks. Weevil larvae feed inside the stems and the adults feed on the leaf buds, therefore they both help to manage the weed. Over a period of one to three years after weevil introduction, the matted Salvinia turns brown and sinks to the bottom of the water body. Preferring open water with little shade, all stages of the weevil’s lifecycle are temperature dependent; therefore, weevils should be released during spring and summer months. Salvinia Weevils are commonly used by landholders in South East Queensland and are available from your Council – just ask your Land for Wildlife Officer.
Equipped with knowledge, the right information and a positive commitment, weed management can help restore and protect the great diversity our riparian areas have to offer.
References & Further Reading
Julian M, McFadyen R and Cullen J (2012) Biological Control of Weeds in Australia. CSIRO Publishing.
Sullivan P & Postle L (2012) Salvinia Biological Control Field Guide. NSW Department of Primary Industries.
Walden D, Boyden J, Bayliss P & Ferdinands K (2012) A preliminary ecological risk assessment of the major weeds on the Magela Creek floodplain, Kakadu National Park. Commonwealth of Australia.
Department of Environment and Heritage (2003) Weeds of National Significance: Weed Management Guide Salvina (Salvinia molesta). CRC Weed Management.
Walton C (2005) Reclaiming Lost Provinces a Century of Weed Biological Control in Queensland. Department of Natural Resources and Mines.
Article by Stephani Grove Land for Wildlife Officer Ipswich City Council
10 responses on “Weevils Help Control Salvinia”
Where can you buy these weevils from do you know?
Hi Gaye. The distribution of biocontrol agents (Salvinia weevil) can only be undertaken with a permit issued under the Qld Biosecurity Act. I suggest that if you live in south-east Queensland, you could contact your local Council and ask to speak to the Environment Officer about sourcing some Salvinia weevils. Most Councils in SEQ hold permits to distribute Salvinia weevil biocontrol agents.
Where can I get hold of the salvinia weevils … The dams on the river flats are full of salvinia this year and is more prolific this year…
If you live in south-east Queensland, try contacting a Land for Wildlife officer in your local Council.
Hi Wayne. The distribution of biocontrol agents (Salvinia weevil) can only be undertaken with a permit issued under the Qld Biosecurity Act. I suggest that if you live in south-east Queensland, you could contact your local Council and ask to speak to the Environment Officer about sourcing some Salvinia weevils. Most Councils in SEQ hold permits to distribute Salvinia weevil biocontrol agents.
We have salvinia in our pond. We live in Louisiana. Who do we contact to buy weevils?
The Sunshine Coast Council no longer has a Salvinia weevil program. Where would be the best place to get the weevil from?
You might wish to try Gympie Landcare https://gympielandcare.org.au/nursery/bio-control-services/
Or the main Brisbane based facility – https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/land-management/health-pests-weeds-diseases/weeds-diseases/invasive-plants/restricted/salvinia
Hi I have a heavy infestation of Salvinia on my dam and would appreciate help with how to begin to eradicate the weed please. I have contacted Gold Coast City Council and have been given the name of a herbicide to spray but I would prefer to find other methods or ideas over spraying. I have also contacted a chap who comes in with equipment but that would’ve become a terribly expensive exercise costing thousands of dollars
I look forward to your reply and would appreciate any help you can give.
Thank you in anticipation
Hi Elizabeth. The Salvinia weevils are probably your best bet, but as the article says, they alone will not eradicate Salvinia. Herbicide plus weevils is generally required. Please contact the Land for Wildlife team at City of Gold Coast if you wish to find out more about Salvinia weevils or control options.