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Summary
A mysterious disease is starting to kill American beeches, one of eastern North America's most important trees, and has spread rapidly from the Great Lakes to New England. But scientists disagree about what is causing the ailment, dubbed beech leaf disease. Some have recently blamed a tiny leaf-eating worm introduced from Asia, but others are skeptical that's the whole story. First observed in 2012, the disease causes leaves to shrivel and develop black stripes. This summer, a plant pathologist announced that a leaf-eating nematode had satisfied Koch's postulates, the criteria for identifying a pathogen as the cause of a disease. But others suggest the worms are simply transmitting a microbial pathogen that is the disease's true cause.
