The invasive and highly aggressive weed Arundo donax (bamboo) is found throughout the Tijuana River Valley. Horses love to eat this “giant grass”, perhaps because it’s distantly related to the sugar cane family. A recent eradication effort is making healthy arundo hard to find. Arundo stands are being sprayed with Round Up mixed with a blue-green dye. It is recommended by a former valley biologist that horses not eat arundo that has been sprayed or appears to be dying.