Controlling Poisonous Tansy Ragwort Keeps Livestock Safe

If tansy ragwort is gaining a foothold in your pasture fields, it’s time to take action.

The poisonous yellow-flowered plant has taken root in pastures and hayfields across North America and its liver-damaging alkaloids can kill livestock, explains Ministry of Agriculture, Food and Rural Affairs weed specialist Mike Cowbrough.

In this video, Cowbrough offers tips on how to best control the weed. The plant’s flowers have 10 petals, stands 30 to 60 centimetres tall, and its leaves resemble kale.

When a small number of the plants are scattered throughout a pasture, Cowbrough says the best option is to simply dig them out, making sure to get the roots. “If we do that, the tansy ragwort plant is going to desiccate and die … and it doesn’t come back.”

When it comes to tackling larger populations, herbicides are the best option — research trials have shown that mowing the weed is ineffective.

With its yellow flowers, tansy ragwort stands 30 to 60 centimetres tall. Its leaves resemble kale.
With its yellow flowers, tansy ragwort stands 30 to 60 centimetres tall. Its leaves resemble kale.

Cowbrough worked with researchers at the University of Guelph’s Ontario Agricultural College to evaluate four herbicides registered to control tansy ragwort. In the video, Cowbrough illustrates how only two of those herbicides – Restore and Milestone – adequately control the weed. Over two years of trials, Milestone has proven to be the most consistent product.

Cowbrough emphasizes that application timing is important when using herbicides to control tansy ragwort. It’s best to spray when the weed is small – less than 10 centimetres tall – and actively growing. Typical timing for this growth stage is early May.

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