This is a common lawn turf grass disease called red thread (also known as Pink Patch) as a result of low fertility, lack of sunlight and drought. There are some simple strategies for treating this issue and one of the most common is to simply maintain your proper fertility levels. Changing your irrigation schedule to longer watering intervals but less frequent while avoiding afternoon watering. Maintaining sharp mower blades along with bagging the grass clipping while mowing to avoid spread is essential. In some cases, inspection of the thatch layer be necessary.