Most weeds that appear to be clover in local lawns are actually oxalis, also known as wood sorrel. These small, perennial plants have 3-parted leaves, yellow flowers, and creep across the lawn. If it weren’t growing in and competing with the turfgrass, it might be considered attractive.
Good control can be achieved by spot spraying the leaf surface with Atrazine, an herbicide available at most garden centers. This product is safe to use on St. Augustine lawns, but should not be applied in summer when temperatures exceed 85 degrees since damage to the turf could occur. 

Additional Resource 

http://edis.ifas.ufl.edu/pdffiles/EP/EP14100.pdf