I need to kill burdocks in my horse pasture.
Go here for a detailed answer to your question from a weed science specialist:
Information at this website may also be of interest:
Fall grazing management affects burdock populations in pastures
Is it too late this fall to apply the 24d?
Maybe or maybe not. Results of using 24d now could depend on weather conditions the next week or so.
The information at this website was prepared for Missouri residents, but it also applies to Minnesota: