Gazanias, introduced from South Africa as ornamental garden plants, are spreading across South Australia and threatening both agricultural land and native vegetation, according to ABC News Australia. The colourful plants outcompete crops and can consume enough soil moisture to prevent cereal crops from surviving.
Researchers from La Trobe University are studying the weed at trial sites in Loxton, in the Riverland, and Arno Bay, on the Eyre Peninsula. The three-year project has received $700,000 from the Grains Research and Development Corporation and is examining the plant’s biology and possible control methods.
Researcher Ali Bajwa said the strongest results came from combining cultivation with herbicide mixtures. Cultivation involves using machinery to rip deeply into the soil and remove the weeds, including their extensive tap roots. Bajwa said the approach had wiped out up to 95 per cent of gazanias in some paddocks, although he acknowledged that cultivation can increase erosion risks and is not desirable for repeated use in some soil types.
The researchers said there is currently no herbicide registered specifically to control gazanias. Farmers are using mixtures of existing herbicides while they wait for possible minor-use permits or registrations. Bajwa said new chemical solutions could potentially become available within the next year or two.
The weed has caused significant problems for Loxton farmer Paul Rudiger, whose gazanias have made some paddocks unviable for cropping after decades of worsening infestations. He told ABC News Australia that cereal crops planted near the weeds die because the gazanias’ roots take the available moisture. Cultivation has helped on some land, but he said the process is intensive and expensive.
Another farmer, Paul Kaesler, said gazanias had moved from nearby irrigation blocks along roadside verges and into his family’s paddocks. He called for faster herbicide approvals and urged the public to comply with South Australian restrictions on selling and moving the plant. Gazanias are declared weeds in South Australia and several other Australian states, while only sterile varieties may be sold within South Australia.