There are some homemade remedies that have been used, like baking soda, that will burn crabgrass, but it comes right back. Asulox was the chemical of choice in 1998 that would kill existing crabgrass. That chemical has since been banned and cannot be used on St Augustine lawns. The best way to control crabgrass is to prevent it from germinating in spring. At Partners in Green we apply 3 pre-emergent treatments, one each in spring, summer, and fall, to prevent weeds from germinating.