It is hard to have a productive conversation about agricultural pesticide use. The subject carries so much ideological baggage that raising it can invite an argument—or bring the conversation to an uncomfortable silence. Glyphosate, the active ingredient most closely associated with the Roundup brand, is the best example. Many people are convinced that it causes cancer, a belief reinforced by highly publicized jury verdicts against Monsanto and its successor, Bayer CropScience. Those verdicts carried considerable legal and financial consequences, but they did not settle the underlying scientific question. The issue is again timely. EPA is approaching an important registration-review milestone for glyphosate and hundreds of other pesti...