Orthene is the best we've found but we treat individual mounds with it.  Can spray it broadcast as well.  Any insecticide will control them though.  The best way is by the mound, as they are constantly producing queens and they usually leave and start new colonies after a rain.  So they're like deer, you can gain on them only by preventing a colony from producing any more.  I've threatened to make dad put in a cheap bifenthrin every trip over beans, from burndown to desiccation to get rid of them.  It works but it's not something you think about till harvest.  The extra wear on a combine is real.