Californian Thistle Control

Controlling californian thistle

To control the thistle, we need to focus on reducing the number of overwintering shoot buds on the creeping roots in the soil. This is where the Cambrilea team will come and spray the Californian Thistle.

For many years, we have significantly reduced large infestations on many clients’ farms using pasture boss, which targets the thistle with a high water rate (blanket/spot spray) in an early summer / too early autumn single application. The aminopyralid in pasture boss also sits in the thistle’s rhizome, preventing further spread.

For more information, contact us to learn how to control your land. 

Californian thistle facts

• A perennial plant that produces thistles from underground growing points every season. Thistles die off as winter approaches. Roots remain in the paddock
• The main method of spread is root growth. Up to 100m of root can be produced from each stem every year to produce a total of up to 4,000km of roots per hectare
• Extensive patches are normally a single plant
• Half of the root mass grows in the top 30cm of soil
• Root chips of 1mm in diameter will grow into new plants that are easily moved by stock or machinery
• Male & female plants growing closely together are required to produce viable seed
• Very low numbers of seeds germinate. The viable seed will only grow in bare, undisturbed, non-shaded soil
• Prefers moist, light loam soils but will grow on pumice or sands with good nutrient levels

A. Thistles above the ground seriously limit pasture production and utilisation and therefore stock productivity.

B. Roots have a large number of growing points every few centimetres along horizontal roots, radiating out several metres from the parent plant, each one capable of growing into a new thistle.

C. Roots below ground: Vertical roots for food storage – Horizontal roots invade more ground and produce more thistles.

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What is Tordon™ PastureBoss™?

Tordon PastureBoss is a new-generation herbicide from Corteva Agriscience™, which is particularly effective at controlling weeds with large root systems, such as Californian thistle. This weed displays only 10% of its biomass above the ground as thistles, while the remaining 90% is a huge underground root system. Above ground, “Calis” have a huge impact on farm productivity, make areas difficult to graze and have a severe effect on grass growth by shading and depleting moisture and nutrients.

In New Zealand, Corteva Agriscience has introduced Tordon PastureBoss as a superior herbicide to replace Versatill™ and other Tordon products to control Californian thistle in the pasture. In independent studies, Tordon PastureBoss was shown to have more herbicidal activity at lower dose rates than Versatill. This is because a larger proportion of Tordon PastureBoss is translocated into the root system, which destroys the growing points. This is critical for long-term control of calis.

Californian thistle is also a major problem on UK farms. Nearly a year after application in 3 trials in the UK, 95% control of Californian thistle was achieved from a single application.

For best results, apply Tordon PastureBoss to actively growing Californian thistles.

Tordon™ PastureBoss™ provides superior control of Californian thistles

Trial Data
Corteva Agriscience conducted Californian thistle trials in the Te Awamutu area during the 2009/10 season. These trials assessed knockdown, brownout and emergence of new aerial stems (thistles) for eight months following spraying.

Tordon PastureBoss provided 92% control of Californian thistle from a single application, over 30% greater than Tordon™ Gold, a previous industry standard.

Figure 1 clearly shows the robustness of Tordon PastureBoss, where even half the label rate exceeded the thistle control of the Picloram + Triclopyr product applied at full rate.

Effectiveness against Californian thistle

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Californian thistles grow well in flat, well-drained fertile sites.

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Large Califonian thistles seven days after application of Tordon PastureBoss.

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The foreground above was treated with Tordon PastureBoss. The background is untreated.

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The image demonstrates the huge root system known to invade the most productive pasture. Tordon PastureBoss translocates throughout the root system aiding in control of unseen growing points developing underground, preventing further reproduction.

Credit: Corteva agriscience

Californian Thistle Control