Ulmus americana 'Princeton'

Ulmus americana
Mature Princeton Elms on the right, planted in the 1920s, with Delaware Elms planted in 1983 on the left. One of the side allées of the Washington Road Elm Allée in Princeton, New Jersey, United States.
Cultivar	'Princeton'
Origin	Princeton, USA

The American Elm cultivar Ulmus americana 'Princeton' was originally selected in 1922 by New Jersey nurseryman William Flemer for its aesthetic merit. By coincidence, 'Princeton' was later found to have a moderate resistance to Dutch elm disease in the USA.

The tree can grow to > 30 m in height, and is distinguished by its dense, symmetrical, upright form and dark green foliage, ultimately forming a broad umbrella crown. Crotch angles can be acute, with considerable bark inclusion which can later lead to branch breakages. The leaves are < 16 cm long by 8 cm broad. 'Princeton' grows quickly, young trees increasing in height by over 1.6 m per annum (d.b.h. by 2.8 cm p.a.) in an assessment at U C Davis as part of the National Elm Trial. The tree commences flowering aged nine years.

'Princeton' leaf

Typical foliage damage sustained in England

Crotch with bark inclusion

Testing in laboratory conditions by the United States Department of Agriculture (USDA) in 1992-1993 revealed that this cultivar has a resistance to Dutch elm disease, although the original Princeton Elm, which grew in Princeton Cemetery and was estimated to be over 150 years old, was felled in April 2005 after suffering 60% dieback, attributed by some accounts to Dutch Elm Disease [3]. Moreover, trees introduced to the UK, where the larger bark beetle Scolytus scolytus is the principal vector, were found to be susceptible, and many died, as did all 20 sent to Eisele, Darmstadt, for testing by inoculation with the pathogen.

Princeton Elms planted in North America are highly prone to leaf damage by Japanese beetles Popillia japonica. Trees grown in the UK have also proven very susceptible to damage by leaf-feeding insects, far more so than native or Asiatic elms. Henry noted that such damage was common to all American Elm Ulmus americana grown in the UK. Trees grown in northern California at U C Davis became infested with leaf curling aphids (Eriosoma), producing copious amounts of honeydew.