Thistles. Everybody seems to have problems with them. To reduce thistles in your fields next year, keep in mind that timing is everything. And October to early November is one of the best times to use herbicides.
Walk out in those areas where you had thistles this summer. I'll bet you find many thistle seedlings. Most thistle seedlings this fall will be small, in a flat, rosette growth form, and they are very sensitive now to certain herbicides. So spray this fall and thistles will not be a big problem next year.
Several herbicides are effective and recommended for thistle control. Maybe the most effective is a newer herbicide called Milestone. Two other very effective herbicides are Tordon 22K and Grazon. But be careful with 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 to the mix.
Other herbicides also help control thistles in pastures like Redeem, Ally and Curtail. 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.