Page "Ulmus americana" Paragraph 31

The few disease-resistant selections made available to the public as yet include ' Valley Forge ', ' New Harmony ', ' Princeton ', ' Jefferson ', and a set of six different clones collectively known as ' American Liberty '.

The United States National Arboretum released ' Valley Forge ' and ' New Harmony ' in late 1995, after screening tests performed in 1992 – 1993 showed both had unusually high levels of resistance to DED.

' Valley Forge ' performed especially well in these tests.

' Princeton ' has been in occasional cultivation since the 1920s, and gained renewed attention after its performance in the same screening tests showed it also to have a high degree of DED resistance.

A later test performed in 2002 – 2003 confirmed the DED resistance of these same three varieties, and that of ' Jefferson '.

' Jefferson ' was released to wholesale nurseries in 2004 and is becoming increasingly available for planting.

Thus far, plantings of these four varieties generally appear to be successful.