Cocoa yields are mushrooming—downward

Hoping to preserve the world’s chocolate output, scientists have begun fighting fire with fire, so to speak—or in this case, fungus with fungus.

Until about 5 years ago, Brazil was the world’s second-leading exporter of cacao, the bean from which cocoa and chocolate are made. Since then, Brazilian cacao yields have nose-dived to about 25 percent of their former level.