Control Pasture Thistles this Fall

Control Pasture Thistles this Fall

Sept. 25, 2015

Figure 1. While the summer-blooming thistle flower (1a, left) may be the most recognizable growth form, scout now for the small, flat rosette stage (Figure 1b) and treat with herbicides this fall to achieve the most effective control.

October and early November is one of the best times to control pasture thistles with herbicides. Delaying treatment until spring can limit your herbicide and control options.

If you had thistles this year, walk out in those infected areas this week.  Look close and you're likely to find many thistle seedlings in a small, flat, rosette growth form. At this stage they are very sensitive to certain herbicides.

Several herbicides are effective and recommended for thistle control.  Several newer herbicides like ForeFront, Milestone, and Chaparral are very effective.  Two other very effective herbicides are Tordon 22K and Grazon. Be careful with all these herbicides, but especially Tordon and Grazon, since they also can kill woody plants, including trees you might want to keep. 2,4-D also works well while it’s warm, but you will get better thistle control by using a little less 2,4-D and adding a small amount of Banvel or dicamba to the mix.

Other herbicides, such as Redeem, Cimarron, and Curtail, also can control thistles in pastures. No matter which weed killer you use, though, be sure to read and follow label instructions, and be sure to spray on time.

Next year, avoid overgrazing your pastures so your grass stands get thicker and compete with any new thistle seedlings.

Bruce Anderson
Extension Forage Specialist

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