Fertilome All Seasons is a favorite for all grasses but especially good for Buffalo Grass.  It will prevent weeds for 3 to 4 months and cost about 1/2 as much as Avert to apply.  It also has fertilizer and does not have to be watered in asap.  It can lay out for up to 21 days as you take time to water it. 

If you don't want to fertilize your grass use Hi Yield Dimension and Gallery.  These are  great weed preventers and can also be put in your flower beds.