Dandy's usually last for severay years, they reseed themselves 3 sometimes 4 times per year and are quite purvasive. To rid your lawn of these flowers, it will be becessary to get at the roots. Mix 3/4 cups of baking powder (not soda) with 1 gallon of water, add 1/2 to 3/4 cups of brown sugar to the mix, spray the flowers with a garden hose attachment designed to disperse fertilizer, spray mid day, the Dandys should be gone in a couuple of days. Here's how it works: Baking powder is a weak mixture of alkali that will kill the roots, the plant will suck it up due to the sugar content in the mixture, grass will be slightly affected, but since grass roots are quite extensive, the grass will recover quite quickly, the roots of the Dandy, on the other hand are not so inter-connected and the plant will die. Do not spray the mixture on plants that you want to save. -Birdy