Striking early visual results from collaborative project

A unique three-way project between supplier, retailer, and farmer is nearing an important milestone as it sets out to prove Californian thistles can be permanently beaten.

After the second herbicide at Simon Campbell’s farm.

While not yet complete, it has already delivered encouraging initial results for those involved, some of whom have been battling Calis for years with limited success.

Corteva AgriScience and PGG Wrightson launched the initiative 12 months ago, recruiting farmers from across the country to follow an expert, staged elimination programme for one of New Zealand’s most expensive, persistent weeds.

The aim? To restore farmer confidence in the fight against Calis, using hard evidence from eight different case study farms implementing best practice control under guidance of local reps.

Marketing manager Nicole Morris leads Corteva’s involvement. She says the last of three herbicide applications will go on soon, after which the focus turns to compiling all the results into a package that documents the whole process from start to finish, so other farmers can pick it up for their own use.

“Most of the sites have had their first two applications – Tordon PastureBoss in summer 2024/25, followed in autumn 25 by Grassmaster MCPA.

“Visually the difference is already striking, but being mindful of Californian thistle’s biology we have to get that third spot spray of Tordon PastureBoss on to any remaining plants this summer to ensure a good outcome.”

That’s because success entails not only an absence of thistles, but restoration of productive grass and clover for grazing.

“We want to prove the financial value of this programme to farmers, as well as the concept,” Morris explains.

So key metrics have been noted at each site for each spray, including the number of thistle stems per square metre, a visual assessment of clover content, and an overall estimation of the thistle infestation per ha.

“Ultimately, we’ll be able to relate that information back to regional pasture productivity, using data in the existing literature.”

Meantime, Corteva and PGG Wrightson hope to be able to run a roadshow with open days at case study farms in early 2026 to start sharing initial results of the programme with a wider audience.

Five of the farms are in the South Island, in North and Mid Canterbury, North Otago, and Southland. The remaining three are in the North Island – Wairarapa, Hawkes Bay and Waikato.

Sheep and beef farmer Simon Campbell’s 520 ha at Mt Bruce is the Wairarapa case study property, and says his family has fought Californian thistles for generations, with some pastures so thickly infested ‘lambs won’t even go in there.’

Campbell recalls his father spent thousands of dollars trying to control the weed, even using a weed wiper attached to the front of his tractor.

However, despite these efforts, the thistles kept coming back. The farm previously wintered cattle, which would clean up thistle patches after flowering, but this approach only addressed the visual nuisance rather than eradicating the problem.

He got involved with the project to improve pasture quality and overall productivity; has treated an initial 30 ha as a result, and is keen to see the final results.

If the three-spray program proves successful, he plans to extend the treatment across the farm in stages.

Nicole Morris says the relationship between local PGG Wrightson technical field representatives and the case study farmers has been pivotal in getting the project up and running.

Joining forces with a retail partner for best practice demonstration like this is a first for Corteva, and a win:win for all involved, she says.

“We know the issue is getting worse; California thistles are spreading and the feedback we’ve been getting is that farmers are becoming disillusioned and losing confidence in their ability to stay on top of them.

“We also realise one of the best ways to promote what can be achieved with a programmed approach control is through using demo sites, and sharing farm case studies.

“But we’re a small team, and we alone don’t have the resources to do this type of extension work at scale, so it made perfect sense to partner with PGG Wrightson on a multi-year national initiative we believe will make a real difference to farmers.”