I have had luck and others have reported success killing them with kindness. Mow, clip or pull as often as you can and apply a heavier than normal application of molasses. Use about 10 lbs per 1000 sq ft and repeat in two weeks. The mixed products that contain molasses, cornmeal and wheat bran will also help. The idea here is to stimulate a furious level of biological activity aimed at rotting the crowns of the undesired plants.