Tim Gottwald will never forget the sight: the mottled yellow leaves, the withered branches, the small, misshapen fruits, tinged with sickly green. These were the signs he’d learned to associate with huanglongbing, or citrus greening—a devastating and wildly infectious bacterial infection that slashed the United States’ orange juice yields by more than 70 percent in the span of a decade.
“It’s like a cancer,” says Gottwald, a plant pathologist with the United States Department of Agriculture. “One that’s metastasized, and can’t be eradicated or cured.”
Once they’ve begun to sport splotchy foliage and stunted fruit, trees can be diagnosed with a single glance. A symptomatic plant, Gottwald says, is a diseased one. Unfortunately, the converse isn’t true: Infected trees can appear normal for months, sometimes years, before visibly deteriorating, leaving researchers with few reliable ways to suss out sick citrus early on—and giving the deadly bacteria ample opportunity to spread unnoticed.
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