If bluegrass music is as American as apple pie, then Leftover Salmon and The Infamous Stringdusters are definitely apple pie à la mode. Over their respective careers, the two wildly innovative groups have topped old musical traditions with sweet, modern flavors, delivering blistering live performances and amassing fervent followings around the world. And to top it all off, they’re both picking August 20 at Ravinia to dish up hearty helpings of their tasty twangs.