Can you harm your grass by using crabgrass control too much/too often ? I have a lawn service (fertilizes, crabgrass control, etc), and they have told me that too much of the crabgrass control can harm the lawn. We're having a terrible time with crabgrass and I've been told to be patient. Most of it is in thin areas but it is also in the thicker areas (not as bad). They have been out 3-4 times to treat but it is still a problem. Do I need to be patient or get a new lawn service?