Rookie mistake was to spray thistle patches with glyphosate. Then, marestail took over. Where did THAT come from??

The plan now is to spend a few years knocking out broadleaf weeds. But this is excellent songbird cover, so I only mow the worst parts in early summer. By July, I'm wondering whether to mow the whole pasture...or go straight to the Grazon? My lack of experience in forages begins to show!  :-)