There are two kinds of plants: grasses and broadleaf plants. Weed b gone kills many broadleaf plants. It does nothing on grassy plants. The weed you have is a grassy plant. You will need a grass killer for that one. Unfortunately your lawn is grass, too, so the grass killer will kill your turf grass.

After you kill the grass and weed, the way to restore the grass depends on what grass you have. If you have Kentucky bluegrass, it will come back by itself. If you have fescue, it must be reseeded, preferably in the fall after the crabgrass has stopped germinating.

Which grass killer would be best? I have heard with Roundup nothing will grow back.

Thank you for your help so far.

Round Up is not permanent. You can reseed two weeks after an application. For killing weeds I prefer some of the off brands and find they actually work better. Round Up's main ingredient is glyphosate but it also contains a chemical for quick results. You spray in the morning and by that evening you already see some wilting. Problem with that is in order to kill the weed the glyphosate needs to be drawn down into the roots by the leaves of the plant. Once the plant is wilted and brown it's not transferring anything to the roots. I use either the Groundworks brand 41% glyphosate from Tractor Supply or the Eliminator brand from Walmart. Neither of these contain the "happy chemical" that kills almost immediately like Round Up. You can expect either of these to take about a week before you see results but by then they have already drawn the glyphosate down to the roots and you get a better kill. I do mix in dish detergent with both of these to help them stick to the plant but overall it's much cheaper with better long term results.

That being said, you can use a small paint brush and paint the glyphosate on the leaves of the weeds. I've done this in the past with great results with little or no damage to the surrounding good grass. Only down side is if you have a lot of weeds it can be extremely time consuming.

I'm no expert in Round Up but I believe the miracle that makes it work better is dish soap...with a more technical name like sodium laurel sulfate.