All Natural Plant Herbicide Pour sugar on plants that you want to kill. Sugar encourages microbes growth. The sugar actually improves the health of your soil long term, but it will cause so much microbe action that the plant/root will overload and die. This is a great way to kill off stubborn thickets or vines, which you keep trimming back. I don't know if this works or not but it's good to know they have found something sugar is good for.