Cottingham Farm's Shane Shewbridge shows off some organic heirloom tomatoes at the U.S. Department of Agriculture (USDA) summer farmers market opening of its 17th season at the USDA Whitten Building east parking lot in Washington, D.C., on Friday, May 31, 2012. This year's theme is Grow, Healthy, Eat Healthy and Be Healthy. USDA and Fuel Up to Play…