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Pest Patrol: How do I control tansy ragwort in my pasture?

#PestPatrol with Mike Cowbrough, OMAFRA

By Kate Ayers
University of Guelph, Ontario Agriculture College

Tansy ragwort is a noxious weed most often found in pastures and hayfields. It is a biennial or short-lived perennial that reproduces through seeds and roots. Tansy is poisonous to livestock and can cause liver damage. Symptoms that may occur after plant consumption include: weakness, high temperature, inco-ordination and yellow mucous membranes. Currently, there is no known antidote for this alkaloid-based toxin.

In Eastern Canada, there are four herbicides which list tansy ragwort on their labels as being controlled: Banvel II (dicamba), 2,4-D Amine 600, Milestone (aminopyralid) and Restore II (aminopyralid/2,4-D). It is unclear, from reading each product’s label, which herbicide would be the most effective at managing tansy ragwort. A trial was conducted to evaluate the performance of each herbicide.

table1-tansy-ragwort-control-options

At the time of application, the majority of the plants was 15 cm tall and 10 to 20 cm in diameter (See figures 1 and 2 below).

Figure 1: Tansy ragwort size at time of application.

Figure 1: Tansy ragwort size at time of application.
photo: Supplied

Figure 2: Tansy ragwort size at time of application.

Figure 2: Tansy ragwort size at time of application.
photo: Supplied

Summary:

Milestone was the most effective herbicide evaluated in 2015. It caused the majority of plants to wilt and die. However, new plant growth has been observed since application but at levels much lower than all other treatments. Digging up tansy ragwort and removing all of the roots was also effective with no observed regrowth throughout the season.

Have a question you want answered? Hashtag #PestPatrol to @cowbrough or email Mike at [email protected].

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