Late in the summer of 2012, while walking his coffee groves on a hillside rising above Santa Ana, El Salvador, Mario Mendoza Corleto noticed something unusual: the leaves on some of his trees were coated with an orange fungus and had begun dropping to the ground. It was “leaf rust,” a form of blight that had pestered coffee farmers in El Salvador since the 1970s. Normally, spraying the trees with fungicide once or twice a year would keep the disease at bay. Not anymore. “This year it was totally different,” Mendoza recounted to me recently. “Spraying didn’t help.”
As the days wore on, the problem only worsened. By September, many of Corleto’s once-bushy trees stood completely bare. Their green fruit hardened in the sun, never ripening into the candy-red cherries that Mendoza’s workers would pick and process into coffee beans destined for specialty roasters. That year, half of the trees on his family’s 100-year-old farm died. The next year, as Mendoza’s remaining trees continued to struggle, he laid off most of his workers. The harvest was a quarter of its usual size.
What happened to Mario Mendoza Corleto played out all across El Salvador, as well as Honduras and Guatemala: ground zero for the Western hemisphere’s most prized coffees.
For the next two years, la roya, as leaf rust is known locally, tore through Latin America’s coffee farms, infecting as much as half of the total acreage, inflicting over $1 billion worth of damage, and helping to trigger a migrant crisis as farmers and farmworkers fled economic ruin.
Coffea arabica is one of the least genetically diverse — and therefore, least resilient — modern crop species on earth.
How did leaf rust suddenly gain the upper hand? Researchers think the disease, a fungus that evolved with coffee trees in the forests of Ethiopia, may have undergone a major recent mutation to become more aggressive. Meanwhile, climate change created the warm, wet weather conditions that sent it into hyperdrive…