Willie Nelson has canceled at least four tour dates scheduled later this month. Concert promoters say Nelson's representatives have cited exhaustion as the reason for the cancellations. They include concerts on Sept. 21 in Lake Ozark, Mo., and Sept. 22 in LaSalle, Ill. Also canceled are shows on Sept. 25 in Sioux City, Iowa, and Sept. 26 in Rapid City, S.D. All four performances were originally scheduled in July but were rescheduled because of Nelson's exhaustion. The 74-year-old Country Music Hall of Fame member performed Sunday (Sept. 9) at the Farm Aid concert in New York City. It was announced last week that Nelson has accepted a role in Swing Vote, a film currently in production featuring Kevin Costner, Kelsey Grammer, Dennis Hopper, Nathan Lane, Stanley Tucci, George Lopez, Richard Petty and others.