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A supercharged solution to dense Californian thistle
Well established, dense Californian thistle is one of the most challenging pasture weeds to control. Once established, this weed displays only 10 percent of its biomass as aboveground thistle stems, while the remainder is an extensive sprawling root system with multiple dormant buds ready to form the next flush of emerging stems. Eradication of Californian thistle relies on designing and implementing a control programme that kills the entire root system, preventing recovery and re-establishment.
Traditional herbicide programmes for Californian thistle control rely primarily on phenoxy chemistry, particularly MCPB and/or MCPA, or 2,4-D, prescribing multiple applications per season across at least two seasons. If followed through, this programme can be successful. While these herbicides are generally less expensive per hectare, repeat application costs and the long path back to fully productive pastures often make this a battle of attrition. In dense populations, this is a tough weed to control using softer, clover-friendly chemistry. Protection of pasture clover content is often seen as a driver for control method and herbicide selection in established pastures and is the obvious benefit of mowing, grazing or the use of phenoxy-based products, particularly MCPB. That’s fine if you are getting worthwhile productivity from clovers. In scenarios where the Californian thistle population is dense, clover performance will typically be severely compromised. This presents an opportunity to supercharge the programme using a herbicide with much higher efficacy on Californian thistle, bringing pasture back into a productive state much quicker. For more than a decade now Tordon™ PastureBoss™ has proven to be the most effective herbicide on Californian thistle. New Zealand trials and field experience consistently show Tordon PastureBoss to achieve up to 30 percent greater control than other registered options. This has a huge impact when incorporated into a control programme for dense Californian thistles. A key contributor to this is the primary active ingredient, aminopyralid, which translocates
| Dense Californian thistle can result in totally unproductive pasture. further into the root system, reaching more root buds and killing them. Thistle stems emerging from surviving root buds are significantly less vigorous, further tiring the root structure. Using Tordon PastureBoss early in a control programme presents a much more aggressive and reliable approach for dense Californian thistle. Californian thistle control programmes can be initiated with an application of Tordon PastureBoss when a good portion of thistle stems reach early bud stage, typically late November to early January. Ground boom spraying is most effective on dense thistles and is the preferred option over carpet or wick type applicators early in the programme. A follow-up treatment using a phenoxy herbicide should be applied to control the next flush of stems in late February or March. This is timed to allow a further emergence of stems which are killed free-of-charge by the onset of winter. With the release from Californian thistle competition, pasture recovery including re-establishment of clover will begin from the next spring. Be sure to spot spray any final emerging stems using Tordon PastureBoss to ensure complete control. Pick your worst Californian thistle paddock and implement the supercharged programme this season.
