Have a stubborn weed? Try boiling water. Boiling water will kill any plant growth it touches. It is very inexpensive and simple to use. Pour the kettle water slowly and from a close height of a few inches above the plant crown to avoid splashing. If a weed resprouts, repeat. Each time the weed resprouts the growth will be smaller and weaker and the most stubborn perennial weeds will eventually die, usually after two or three treatments.