I hate to say it but you have a weed taking over your lawn that is known as Creeping Charlie. I know of no means of getting rid of it short of chemically killing your entire lawn and starting over. There may be something out there that I haven't heard of though. Some folks actually grow it as a ground cover.
So sad to see hit this advice is what must happen!
Thank you Chuck. I appreciate you taking the time to respond. Darn. Maybe dig it out and restart in these areas ...
CC is a type of mint. It spreads by seeds, by rhizomes and stem cuttings. The only way to dig it out would be to remove your soil. I think you would be better off just using chemicals, but even then what's to stop it from coming back at some other time?
I doubt if reseeding would help. You will probably have to research which chemicals kill CC but does not harm grasses. IIRC Crossbow herbicide will work but not sure on this. There is really no feasible alternative that I can think off.
The spreading bit by chopping with a mower or weed eater is what really spreads it. I have CC and another called Speedwell that both propagate by chopped parts. One borrowed piece of equipment, rented or otherwise for example and you are "infected" for all practical purposes.
It would take some thought and work but there is one way to solve the problem without chemicals. You could solarize a portion of your lawn and then another until it was gone and you would have new grass too.
