WEED PROFILE – Californian Thistle Weed Control
Californian Thistle (Cirsium arvense) is a common and persistent problem in New Zealand pastures. Often called the “Cali” thistle, it spreads through a creeping root system. This makes the thistle tough to control, as it outcompetes pasture plants and is avoided by livestock due to its spiny foliage.
Ag Research NZ has stated that the true cost of Californian thistle is close to $700 Million in lost pastoral farm revenue each year. They also suggest that previous estimates of the cost of other agricultural weeds have been significantly underestimated!
The Weed
Unlike other thistle species in New Zealand, Californian thistle is a perennial with a creeping root system that connects its plants that grow in patches. A cluster of these thistles usually comes from a single root, making them effectively one plant. In some cases, an entire paddock can consist of one massive thistle.
The above-ground parts die off in late autumn or winter, but the roots stay alive and sprout new growth in spring. Because of this extensive root system, Californian thistles are tough to eliminate, and one treatment often isn’t enough for great weed control.
One of the most effective ways to control Californian thistle in pasture is to use the Redback Weedwiper. The Redback Weedwiper’s thick carpet wicks apply the herbicide directly to the thistle foliage without touching the surrounding pasture.
For The Best Results
We recommend grazing your pasture as low as possible before applying your herbicide with a Redback Weedwiper so that the wiper can be set as low as possible. Hit any really thick patches more than once!
The best time to use a weedwiper is in late summer or early autumn when the plants are actively growing, and sugars are moving down to the root system. Avoid wiping when the thistles are stressed, as control may be less effective. Regular mowing can also help weaken the thistle’s roots, but it needs to be done consistently for lasting results.
Weed Wiper Californian Thistle Effectiveness Research
Dr. Kerry Harrington is a weed science expert from New Zealand who thinks that Californian thistle (called perennial thistle in Australia) is one of the biggest threats to pastures in New Zealand. While working at Massey University, he discovered that the most effective herbicides, like glyphosate, can kill the thistle’s roots but also harm the desirable plants in pastures if sprayed directly.
To find a better solution, Dr. Harrington studied how well weed wipers could target thistles without harming other plants. He tested different herbicides by counting the number of thistle stems in specific areas before treatment and then checking those areas regularly for a year. This helped him see how well the weed wipers worked at killing thistles while keeping the rest of the pasture healthy.
His research found that the best treatment was a mix of 1 part Glyphosate 360 and 20 parts water, applied in autumn. This mixture did not harm clovers, unlike other herbicides, clopyralid and metsulfuron, which could damage clover if it rained soon after being applied.
How effective Is weed wiping the Californian Thistle?
Weed wiping is a highly effective way to control Californian thistles for two main reasons.
- Some herbicides are really effective and can target the thistle at any growth stage while it is safe, easy to apply, and cost-effective. However, those same herbicides can’t be sprayed to pastures because they will damage grass and clover.
- Since Californian thistles grow upright, a large portion of their foliage extends into the wiping zone, well above the pasture, making it easier to apply the herbicide effectively.
Weed Wiper Herbicide Advice For Californian Thistles
We recommend talking to your local chemical specialist or agronomist to find the best weed control chemical solution and mix for weed control as they are the experts! However, here are a few herbicides our customers have told us they have used to kill Californian thistles.
MSF600 applied at 50g/10L of water.
Glyphosate 360 at 5% or 500ml/10L water. Glyphosate 540 at 333ml/10L water or Granny granular glyphosate at 225g/10L water
MSF600 at 25g/10L water plus either Glyphosate 360 at 250ml/10L, Glyphosate 540 at 170ml/10L water or Granny granular glyphosate at 110g/10L
FINAL WORDS
In summary, Californian thistle is a significant and challenging weed in New Zealand pastures, primarily due to its extensive creeping root system that allows it to spread rapidly. The Redback Weedwiper provides an effective weed control solution for this persistent problem by delivering targeted herbicide application directly to the thistle while minimising damage to surrounding pasture plants. With the insights from experts like Dr Kerry Harrington, farmers can make informed decisions about herbicide use and control strategies, ensuring healthier pastures and more effective management of Californian thistle.
We’d love to hear your thoughts! If you have any feedback, comments, or questions about managing Californian thistle or using the Redback Weedwiper, please feel free to reach out. Your insights and experiences are valuable to us and can help others facing similar challenges!
You may also like to check out our other pasture improvement products such as the Redback Triangle & Chain Harrows, Cover Harrows, Cultivators and Rollers.