By Elisabeth Malkin The New York Times May 5, 2014 Four million people in Central America and southern Mexico rely on coffee for their living, and coffee rust is a major threat. Credit Janet Jarman for The New York Times SAN LUCAS TOLIMÁN, Guatemala — When coffee rust attacked the farms clinging to the volcanic slopes above this Mayan town, the disease was unsparing, reducing mountainside rows of coffee trees to lattices of gray twigs. During last year’s harvest, Román Lec, who grows coffee on a few acres here, lost half his crop. This year, he borrowed about $2,000 for fertilizer and fungicide to protect the plants, as he did last year. But the disease returned and he lost even more. “There are nights when you cannot sleep, thinking how to pay back the money,” said Mr. Lec, 65. A plant-choking fungus called coffee rust, or la roya, has swept across Central America, withering trees and slashing production everywhere. As exports have p...