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An article in The Journal of Arboriculture for March 2004 reports results of a study on elm tree diseases that was started in 1990 in Holbrook Palmer Park.
From 1978 to 1991 fifty-two elm trees were removed from the park due to Dutch elm disease. Thousands of elms have been lost throughout the bay area. Because elms can otherwise thrive in urban environments and the elm’s arching branches can be beautiful, town residents have an important stake in finding elm trees that can resist the disease and thrive in Atherton’s Mediterranean climate.
Earlier research in the east had identified elm cultivars that resisted Dutch elm disease but it was not clear how well these cultivars would do in Northern California. A cultivar is a clone of an individual tree, usually propagated from a cutting of the original tree or an earlier clone of it. In the study, sponsored by the University of California and the U.S. Department of Agriculture, four different cultivars and a standard American elm were planted in each of fifteen “blocks”.
Among the seventy-five trees planted, only one, an “American Liberty” cultivar, contracted Dutch elm disease. The cultivar that grew to the greatest average height was named “Frontier”, making it probably the best selection for Atherton landscapes. As a bonus, “Frontier” has a beautiful burgundy fall color. “Frontier” and “Prospector” showed superior resistance to elm leaf beetle but “Prospector” required expert pruning, grew to only 65% of the height of “Frontier”, and developed a round-headed form unlike the familiar American elm. A cultivar successful in the east, “Valley Forge”, grew extremely fast but developed too poor a structure to be suitable for the peninsula.
Atherton was the perfect site for the study. The estate that Olive Holbrook-Palmer donated to create the park had a name of its own. The estate’s name was “Elmwood”.
