Californian Thistle Season: Time for Action
Autumn is when Californian (otherwise known as Cali) thistle starts to take an invasive hold across New Zealand's farms. Now is the time for action to eradicate this particularly noxious weed. A successful control programme requires a well-timed, three-shot approach over the course of a year.
First application
Tordon™ PastureBoss™ is the premium herbicide to use at the front end of a Cali thistle control programme when thistle shoots reach early bud (hard ball) stage, typically late November to early January. Tordon PastureBoss has proven to be the most effective herbicide on Cali thistle for more than a decade. New Zealand trials show farmers gain 92 percent control from a single application of Tordon PastureBoss.
Ground boom spraying is most effective on dense thistles and is the preferred option over carpet or wick type applicators early in the control programme.
Second application
Begin your follow-up treatment in late February or March when the thistles are knee high, and the rhizomatous root system is sending up new shoots. Apply a second round of herbicide,
featuring phenoxy, such as GrassMaster MCPA. This ensures there is adequate green leaf area to absorb the herbicide allowing for maximum translocation down to the root system. Spraying too early, before enough of the shoots have emerged, will reduce absorption of the herbicide. So, timing is everything. While a further emergence of shoots may occur, they will be killed free-of-charge by the onset of winter and frost.
Third application
The third and final application of Tordon PastureBoss should occur the following summer. Targeted spot spraying of any final emerging shoots will ensure complete control by preventing recovery of the root system and reestablishment of Cali thistle.
If you are starting your Cali thistle control programme this autumn, Tordon PastureBoss should be your first weapon with the application providing an initial strong knockdown. Follow with a phenoxy (GrassMaster MCPA) application in spring and implement a spot spray application of Tordon PastureBoss the following autumn.
In late 2024, PGG Wrightson and Corteva Agriscience embarked upon a collaborative partnership to find a permanent solution for Cali thistle. This vital project will run for approximately 18 months.
Follow this journey in Rural Diary.
Registered pursuant to the ACVM Act 1997. Tordon PastureBoss P008205, GrassMaster P009698
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