Which vision of agriculture is right for the farmers of sub-Saharan Africa? Today, says Nigel Taylor, a geneticist at the Donald Danforth Plant Science Center in St. Louis, Missouri, the brown streak virus has the potential to cause another cassava famine. “It has become an epidemic in the last five to ten years, and it’s getting worse,” he says. “With higher temperatures, the whitefly’s range is expanding. The great concern is that brown streak is starting to move into central Africa, and if it hits the massive cassava-growing areas of West Africa, you’ve got a major food-security issue.”