In 2005, the latest variety of American Elm tree, named ‘Jefferson’ was released jointly by the ARS (American Research Service) and the US National Park Service (NPS), after collaborative screening tests this variety was found to have an outstanding level of DED tolerance. It was cloned in 1993 from a single tree that survived DED out of 300 Elm trees planted on the National Mall in Southwest Washington in the 1930s. The DED fungus Ophiostoma ulmi has killed more than 75 million American Elm trees since the introduction of the disease from France.
The variety ‘Jefferson’ grows in the typical vase shape up to nearly 70 feet tall, has broad U-shaped branch unions, and has leaves that turn dark-green earlier in the spring. The leaves stay dark-green later in the autumn than most other elms. ‘Jefferson’ is considered a good ‘street tree’ also because it can withstand pollution from city traffic and has wide adaptability, growing in USDA hardiness zones 5 through 7. The new variety is currently being propagated and it will be 2-3 years before plants are freely available commercially. Alfredo Flores www.usna.usda.gov www.ars.usda.gov |
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