A method of organically controlling crab grass is to burn the young plants with a handheld weed torch. Typically a small control knob regulates the flame size and intensity on the onboard propane canister. Most handheld weed torches are small and easy to manipulate in a garden area or small lawn. An advantage of using a weed torch is that you can concentrate the flame on the crab grass for a few seconds, and it will begin to wilt and die immediately.
Insert the propane or butane canister onto the weed torch. Various models use either of these types of fuel. Follow the manufacturer's instructions for installing the gas canister and lighting the unit.
Adjust the torch to get the smallest, hottest flame. Typically, the bluer the flame, the hotter it is.
Hold the flame on the crab grass just long enough until the plant shows signs of wilting. In most cases, with the flame adjusted correctly, it will take 3 to 4 seconds.
Check the area 24 hours later. The plants should be extremely wilted, if not brown and dry.
Apply the weed torch to any crab grass that has not fully dried out. It will take a little practice with your particular brand of weed torch, as the output on various brands different in both heat and flame size.