I have a small hay field, growing alfalfa, timothy and clover. I have two invasive weeds, one that thick-stemmed broadleaf (I enclosed two photos of this plant) and grows up to 2 feet, crabgrass and the common mustard plant. They are becoming dangerously invasive into the rest of the hay field. I suspect they started from neighbors. How can I control these weeds as there are too many to hack out by hand. Can I use a weed killer and what kind that would not be dangerous once the grass is cut and fed to my horses.