Increased rainfall boosts South Australian crops but spreads invasive gazania weed

More rainfall across South Australia, yielding one of the best cropping seasons on record for farmers, has also helped to spread of one of their worst enemies: gazanias.

Introduced from South Africa in the 1950s and 1970s as an ornamental garden plant, gazanias are a declared weed in South Australia, Victoria, New South Wales, Tasmania and Queensland.

Researchers from La Trobe University have been conducting trials on farms in South Australia's Riverland at Loxton and on the Eyre Peninsula at Arno Bay to understand the pest plant's biology and how to control it.

"[They] are also spreading into some desirable native ecosystems where we have some species that are high value from [a] conservation point of view."

The Grains Research and Development Corporation (GRDC) has invested $700,000 into the three-year project, with earlier work revealing the extensive spread of the weed across southern Australia and parts of Western Australia.

Dr Bajwa said the best results in managing gazanias had been a combination of cultivation, which means using machinery to rip deeply into the soil to pull out the weeds, and then spraying herbicide mixtures.

"While cultivation is not desirable in these soil types and the sort of erosion risk or other environmental factors that can come with that, if we use it strategically once in a while that can potentially be a good option," he said.

Dr Bajwa said there was no registered product to control gazanias, with farmers using a mixture of herbicides to fight them.

"We're getting some very good results and hopefully within [the] next year or two we could be potentially seeing some minor use permits or potential registrations for this particular weed," he said.

Ripping at the roots

Gazanias have rendered some of Loxton farmer Paul Rudiger's paddocks unviable for cropping, which is a blow amid a great season following years of drought.

"The crop, the cereal we sow around them will actually die because with their [the gazanias'] root system they take all the moisture," he said.

While cultivation was intensive on the land and expensive to perform, Mr Rudiger said it was controlling the pest weeds enough to allow his crop to grow.

Spray delay

Up the road, Paul Kaesler is using cultivation and sprays to get rid of gazanias at the farm his family has worked for more than a century.

While Mr Kaesler is pleased the trials have yielded promising results, he is concerned that approvals for new herbicides are taking too long.

"I think that needs to speed up in some way or another or else they will be across the whole state before everyone knows," he said.

In the interim, he said it was important the public adhered to restrictions banning the sale and movement of gazanias in South Australia.

"We still have people come through and go, 'Oh, I'm going to put them in my garden,'" Mr Kaesler said.