Ephraim is a trained heifer that loves to thresh; So I will put a yoke on her beautiful neck. I will set a rider on Ephraim. Judah will plow. Jacob will break his clods.
So, because they had broken the covenant with God, they were swearing falsely when they made that covenant with God, thus God's judgment is gonna spring up upon them, just like weeds, the poison weed of hemlock just grows up in the fields.