A 10-YEAR EVALUATION OF THE PERFORMANCE OF FOUR ELM CULTIVARS IN CALIFORNIA, U.S

In 1992, three elm (Ulmus spp.) cultivars reported to have tolerance to Dutch elm disease (DED) were planted in a field plot in Atherton, California, U.S. Cultivars included 'Prospector', 'Frontier', and 'American Liberty'. A fourth cultivar, 'Valley Forge', was added to the plot in 1999. American elms grown from seed were planted as controls. In the 10-year period from 1992 to 2002, tree height and trunk diameter were measured annually, and inspections for DED infections, elm leaf beetle activity, and other pests were conducted. In August 2003, one 'American Liberty' was found to be infected with DED. This is the only tree that has shown infection symptoms since the beginning of the study. Elm leaf beetle activity was highest in 1993 and 1994, causing substantial injury to 'American Liberty', 'Frontier', and controls. 'Prospector' sustained little injury. Other pest activity has been slight in most years. In 2002, 'Frontier', 'American Liberty', and controls were found to have equivalent trunk diameter growth, and all were significantly larger than 'Prospector'. After 10 years, 'Frontier' was tallest (11.3 m (37 ft)), 'Prospector' was shortest (6.9 m (23 ft)), and 'American Liberty' and controls were in between (9.6 and 10.3 m (32 and 34 ft), respectively). 'Valley Forge' was monitored for 3 years and then removed from the study because of poor structure.