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Double Jeopardy for Elms Dutch Elm Disease and Phloem Necrosis by DAVID F KARNOSKY American elm Ulmus americana populations across the United States are in double jeopardy The Dutch elm disease caused by the fungus Ceratocystis ulmi continues to spread in North America and has developed more aggressive strains in recent years Now a second major disease is threatening elms Called phloem necrosis it is caused by mycoplasma like organisms Dutch Elm Disease Dutch elm disease is a vascular wilt disease transmitted primarily It was first found in northwestern Europe around 1918 The disease was identified and the causal agent described by Dutch scientists Rather unfortunately for the Dutch the common name for the disease came to be Dutch elm disease Actually the disease is thought to have originated in the Far East By 1939 Dutch elm disease had spread rapidly across Europe killing over 50 of the elms in Holland alone The Dutch countryside was particularly vulnerable to the ravages of Dutch elm disease because the vast majority of elms planted in Holland belonged to one susceptible clone Ulmus x hollandica Belgica by bark beetles 1 New York Botanical Garden Cary Arboretum Millbrook New York 12545 A specimen American elm Ulmus amencana tree showing the vase characteristic of the specees Photo by D F Karnosky shaped crown The first report of Dutch elm disease in North America came from Ohio about 1930 The causal fungus and its primary vector the small European elm bark beetle Scolytus rnultistriatus had been carried to the United States on elm logs imported from Europe The knots in its wood made it popular for making a burled veneer for furniture Large ports and the railroads that transported the logs inland were the points of entry and routes of spread of the disease After its rapid initial sweep across Europe and apart from local flareups Dutch elm disease came to be regarded there as an endemic disease of little importance However this tranquil situation came to an abrupt

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