Science: Coffee Nerves in Brazil

Of the 375 diseases that can afflict the coffee tree, the most devastating is caused by a yellow-orange fungus called Hemileia vastatrix. In the late 19th century, when it ravaged the coffee plantations of Ceylon and India, the fungus helped change Britain into a nation of tea drinkers. Now it has invaded the New World, spreading rapidly through a Texas-sized area of southeastern Brazil and threatening 2 billion plants that yield a third of the world's coffee.

H. vastatrix's deadly advance has given growers throughout Latin America a bad case of coffee nerves. Once the microscopic spores of the fungus settle on...