Emmylou Harris, John Mayer, Widespread Panic and folk legend Arlo Guthrie have been added to the list of performers at the 20th annual Farm Aid concert, organizers announced Thursday (July 28). The Sept. 18 event at the Tweeter Center near Chicago will also feature Kenny Chesney, Los Lonely Boys, Wilco and blues greats Buddy Guy and Susan Tedeschi. The event will be hosted by Farm Aid board member Dave Matthews and founders Willie Nelson, Neil Young and John Mellencamp.