Chipotle Mexican Grill Inc. sank the most since its 2006 IPO on second-quarter sales that trailed estimates. Slower US consumer spending hurt sales with smaller gains as the year proceeded, finance chief Jack Hartung said. Extreme weather may boost food costs later this year and next, Hartung said. “If consumer spending slows further, a further slowdown in Chipotle” comparable sales is likely, wrote an analyst with Raymond James & Associates in Atlanta. Second-quarter revenue increased 21 percent to $690.9 million, the company said, coming in shy of the $707.3 million estimated by analysts. Chipotle has sought to boost sales by touting sustainably raised and locally sourced ingredients.