Ulmus americana 'Washington'
The tree has been described as possibly having triploid chromosome levels (unusual for an American Elm), suggesting it may be a hybrid between the tetraploid and rarer diploid forms of American Elm, like the cultivar 'Jefferson'.
Pests and diseases
The tree is resistant to Dutch elm disease, but less so than other recent American Elm cultivars such as 'Valley Forge'. Like all other American Elm cultivars, it is also susceptible to Elm Yellows. No other specific information available, but the species generally is also moderately preferred for feeding and reproduction by the adult Elm Leaf Beetle Xanthogaleruca luteola  , and highly preferred for feeding by the Japanese Beetle Popillia japonica    in the United States. U. americana is the most susceptible of all the elms to verticillium wilt.
- http://fletcher.ces.state.nc.us/programs/nursery/metria/metria11/warren/elm.htm Return of the Elm -the status of elms in the nursery industry in 2000. Warren, K., J. Frank Schmidt and Co.
- Miller, F. and Ware, G. (2001). Resistance of Temperate Chinese Elms (Ulmuss spp.) to Feeding of the Adult Elm Leaf Beetle (Coleoptera: Chrysomelidae). Journal of Economic Entomology 94 (1): 162–166. 2001. Entom. Soc.of America.
- Miller, F., Ware, G. and Jackson, J. (2001). Preference of Temperate Chinese Elms (Ulmuss spp.) for the Feeding of the Japanese Beetle (Coleoptera: Scarabaeidae). Journal of Economic Entomology 94 (2). 445–448. 2001. Entom. Soc.of America.
- Pegg, G. F. & Brady, B. L. (2002). Verticillium Wilts. CABI Publishing. ISBN 0-85199-529-2