Most of America’s soybean farmers have been using a herbicide called Dicamba, made to protect specific genetically-modified seeds.  But Dicamba is volatile and drifts across fencelines, killing neighboring soybean crops not seeded for Dicamba. And now, evidence suggests, the Dicamba is also killing many trees across the Midwest, from the Dakotas to Arkansas. Johnathan Hettinger of the Midwest Center for Investigative Reporting has the story.