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A tree infected with the cinnamomi fungus | Courtesy of Linda Haugen/USDA Forest Service/Bugwood.orgThe Fraser fir is the ideal Christmas tree. Fragrant, strong-limbed, and long-lasting when cut, it has found its way to the White House’s Blue Room more than any other tree over the past 50 years. It is also a vector to the most destructive plant pathogen you’ve never heard of.The shapely Fraser fir, a southern Appalachian native now farmed extensively in nurseries, is a common carrier (and victim) of Phytophthora cinnamomi, a deadly water mold wreaking havoc on ecosystems around the world. When infected Frasers are replanted, the disease gets an opportunity to spread to new farms and neighboring plant life.Originating in Papua New Guinea, soil-borne cinnamomi arrived in the United States at least 200 years ago via agricultural trade. The root-rot that it causes transformed the forests of the Southeast, killing huge numbers of American chestnut and shortleaf pine. Scientists didn’t pinpoint it as the source of this dieback until 1948, by which time it was ubiquitous in the South.A cousin of the sudden oak death fungus devastating forests on the West Coast, cinnamomi now affects hundreds of plant and tree species on six continents. In recent decades it has marched westward, killing rare manzanita in California and native oaks in Mexico. It also thrives in avocado orchards, and in fact is the limiting factor in avocado production worldwide.“Cinnamomi continues to get worse. It shows up in new places and on new hosts,” says Everett Hansen, an emeritus professor of botany and plant pathology at Oregon State University who’s been studying the fungus for 30 years. Climate change may open up vast new regions to the pathogen, including in Hansen’s home state. “There’s evidence of cinnamomi becoming increasingly active in areas farther north than it has historically been present,” he says.There is no cure for the fungus, but tree farmers and nursery owners can limit its spread by avoiding the transport of contaminated soil and not letting water pool in affected areas. You might also think twice about replanting that living Christmas tree, especially if it’s a Fraser, balsam, or noble fir. —Nate SeltenrichNEXT: Thou Shalt Not Smite Thy ManateeEdward  R. Max
Max’s Greener Places 

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