You have to use two herbicide separately. If then, you need to waste money and labor.
But, You can use one herbicide over bermudagrass and centipedegrass together.
Caliente Herbicide will be answer.
http://www.pestrong.com/1099-caliente-wdg-herbicide-fast-weed-killer-2-oz.html
Caliente WDG can be used over bermudagrass, St. Augustine, zoysiagrass, centipedegrass, Kentucky bluegrass and fine fescue only.
Rate
0.25 oz ~ 1 oz per Acre. This 2 oz can cover up to 8 acres.
For Backpack sprayer, mix 0.005 oz ~ 0.05 oz by using included scoop per gallon of water.
Label
http://www.pestrong.com/file/1473-Caliente_Label
This herbicide works fast then other normal herbicide.
This will save time and cost.