Salvinia weevils successful in killing invasive water weed


Seven months after Byron Shire Council and Rous County Council released thousands of weevils in the lake at Waterlily Park, the Salvinia weed is almost gone and not a drop of herbicide was used.

The Salvinia weevil is bred by the NSW Department of Primary Industries for use as a biological control for invasive water weeds like Salvinia molesta which, in September 2018, covered the lake at Waterlily Park at Ocean Shores.

When weeds take over aquatic environments they raise water temperatures and deplete oxygen levels which can lead to a fish kill and can also impact on dependent fauna such as water fowl and reptiles.

Andy Erskine, Council’s Open Space Technical Officer, said the weevils have been much more successful than originally expected with most of the Salvinia weed gone and the lake now covered in a native floating fern called Azolla.

The Salvina was so thick on the lake last July that Council had to get mechanical harvesters in to get rid of some of the weed in preparation for the release of the weevils in September.

“At the time Council really only had two options for the ongoing control of the Salvina – chemicals or the weevil,” Mr Erskine said.

“We know that many of our residents are concerned about the use of chemicals in the environment so that’s why we decided to test the effectiveness of weevils and they have been an outstanding success.

“Some people are however seeing the Azolla and assuming this is the Salvinia weed and its important for them to recognise that this is a native aquatic plant and not an invasive weed,” Mr Erskine said.

“The native Azolla will turn red as it matures and then dissipate and sink before Spring,” he said.

“We are thrilled with this result as we now have a known non-chemical treatment for the weeds at this site.”

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