Devastating fungus has already stripped shrubbery in Europe and New Zealand. Shrubs may be trembling by doorsteps across North America as an aggressive fungus disease of boxwood invades the continent. Boxwood blight, caused by a Cylindrocladium fungus, was unknown to science before 2000 but has now spread through Europe and New Zealand. In October, U.S. authorities confirmed that the blight had jumped continents, with infections confirmed in North Carolina and Connecticut. By mid-January, with growers and pathologists on alert, the fungus had turned up in at least five more states — Virginia, Maryland, Rhode Island, Massachusetts and Oregon — and...