You more than likely have purple nutsedge infesting your lawn. I assume that you have bermudagrass and will you be overseeding it with ryegrass for the winter? If so, now is the time to do so and I would suggest that you prep and drop seed. If not, now is the nearing the end of the season to use an herbicide, SedgeHammer, Monument, or Certainty. All 3 work well when applied first around the 4th of July followed by a second application in mid-August at 4-6 weeks later. A single application now while its still warm and the sedge is growing will enable the herbicide to penetrate the leaves and to be moved to the roots and developing tubers that will grow next summer. The herbicide should reduce the ability of the “baby” tubers to develop and reduce next year’s crop. The process will take 3-4 years of diligent effort. In the spring, when the nutsedge begins to appear in March or so, keep putting stress on it by frequent mowing to cut off the new emerging leaves. Water the lawn enough to grow it as nutsedge loves water and wet soils. There is an article available but what I’ve described above should suffice for the lawn treatment.
