A malfunction on a tractor-towed hop-stringing cart injured seven farm workers Thursday morning, some of whom are in critical condition. St. Paul Fire District firefighters responded to an incident at a hops farm field in the 15500 block of River Road northeast of St. Paul at about 10 a.m. Thursday. Responders found a crew of farm workers that had been working on an elevated cart used to hang hops to dry when a malfunction caused the cart and workers to fall. The driver of the tractor was also injured, Assistant Fire Chief Dan Mullen reported.