What Happens When Weed Killers Stop Killing?

Farmers in the United States are heading for a crisis. In parts of the country, weeds resistant to the world's most popular herbicide, glyphosate, now grow in the vast majority of soybean, cotton, and corn fields. Weeds that can shrug off multiple other herbicides are also on the rise. At an American Chemical Society symposium, chemists said they have little to offer: Few new weed killers are near commercialization, and none with a novel molecular mode of action for which there is no resistance.