Published on 08/12/2020
"I think the focus on Calis has dropped off a bit - some people may have forgotten about that programmed approach to control,” says Glen Surgenor, marketing manager for Corteva Agriscience™.“ As you drive round the country over summer, every year the population seems to be bigger than the year before.”
Widespread pasture stress during the dry last season has not helped.
So this season Corteva Agriscience has brought Californian thistles back to the front and centre of its communications to farmers and resellers about maintaining profitable, productive pastures. The company has recently compiled a new technical guide that offers a 101 walk through and reminder about staged herbicide applications to provide a permanent solution to one of New Zealand farming’s most expensive and persistent weeds.
And the story starts right now for resellers and reps whose clients need to get on top of their Calis. “The timing of that first spray in November or December is critical,” Surgenor says. “If you get that right, and then follow up again with a second application in autumn, you’re well on yourway to getting on top of them.”
Tordon PastureBoss is the best option, especially for dense infestations. The withholding periods are relatively short (three days for milk; seven days for meat) and although it will damage clover, pasture production and grazing is already much reduced where thistle populations are high, and that ground will be regained the following season, he says.
A two-spray programme can begin in autumn, but now is a better time to start because of the plant’s natural growth cycle .“The reason we recommend spraying in early summer, after bud formation but before flowering, is that this hard-ball stage coincides with the time that sugars within the plant are actively being sent down into the root system, helping deliver the chemical throughout the plant. “Once flowering occurs, the movement of sugars stays within the upper part of the plant, namely the flowers, limiting distribution of chemical into the root zone, and significantly reducing the effectiveness of your spray application.”
Californian thistle has an aggressive rhizomatous root system, capable of extending more than two metres deep, and producing offshoots that then become new plants, so the importance of getting chemical to this part of the plant cannot be understated, he says. “Up to 100 metres of root can be produced from each stem, every ear, to produce a total of up to 4000 km of roots per ha. What you see above ground is only 10 percent of the plant – all the rest is underground. That’s the main reasons Calis can be so discouraging and difficult to eradicate.”
That’s also the reason a second spray is recommended in autumn, to clean up any regrowth from the root system. “Even a single spray of Tordon PastureBoss is highly effective, and helps to restore pasture productivity in the short term. But we always recommend a follow-up in autumn if required– Californian thistle is very good at finding ways to survive given even the slightest chance.”
Surgenor says Corteva Agriscience trials in the Waikato assessed Tordon PastureBoss for knockdown, brownout and emergence of new aerial stems for eight months following spraying. The herbicide provided 92 percent control of Californian thistle from a single application. Plantback intervals after extensive spot spraying or boom spraying with Tordon PastureBoss are six months for legumes and chicory; three months for forage brassicas and one month for maize.
For more detail contact your Corteva Agriscience territory sales manager.