Dicamba is a herbicide. It kills not only what farmers call broadleaf plants, which include many weeds, but also crops like soybeans. Not these soybeans, though. Monsanto tweaked the genes of these varieties, and now dicamba doesn't bother them at all.
The dicamba era arrived last summer. Farmers sprayed the chemical on their fields and say it worked splendidly. The problem was that when the weather turned hot, the weedkiller didn't stay where it was supposed to. It seemed to evaporate and drift, sometimes for a mile or more, into fields of other crops that can't tolerate dicamba. It left those crops stunted or with curled up leaves.