Ortho makes a liquid crabgrass killer in concentrate and spray bottle form.I suspect other companies do as well.As mentioned crabgrass will begin dying off soon.The real solution is preemergent crabgrass killers (available with and without fertilizer) which are applied in very late winter or very early spring with a second application usually applied around 4-6 weeks later.Your location will influence the timing of these applications.Go to a retailer with qualified help to assist you in determining the right time to apply.

Be sure to hit the lawn with a crabgrass with a preventer in the early spring (aproximately mid-march). The dead crab grass will leave their seeds there to grow in the spring. You'll want to prevent that from happening.

I had that happen, I neglected the first application and I went from the best looking lawn on the block one year, to the worst just from neglecting the first application. Weed seeds travel!!! :(