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<br />How to Identify and Manage Dutch Elm Disease <br /> <br />Page 12 of 16 <br /> <br />Since infection may be more <br />advanced than symptoms indicate, it is important to peel off the bark of infected branches <br />and locate the staining, which indicates the presence of the fungus. All infected branches <br />should be removed at a branch fork at least 5 feet, and preferably 10 feet, below the last sign <br />of streaking in the sapwood (figure 8). Whenever elm branches are pruned during the <br />growing season, pruning paint specifically formulated for use on trees should be applied to <br />prevent attraction of elm bark beetles to the wounded trees. (painting tree wounds is <br />generally not recommended, except to prevent disease transmission in oaks and elms.) <br /> <br />Pruning is more likely to be effective if augmented by systemic injection of fungicides. <br />Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree, <br />although all dead branches should eventually be removed. Whereas pruning alone is not <br />effective against residual infections, fungicide injection may be. If fungicides are used, they <br />should be injected prior to removal of diseased branches. The keys to successful eradicative <br />treatment are early detection and prompt treatment <br /> <br />Planting Dutch Elm Disease resistant or tolerant trees. Planting trees with resistance or <br />tolerance to DED is a valid management option. However, selecting only a few cu1tivars <br />limits the genetic variability of the population. This could lead to increased risk of <br />widespread losses if these cultivars are found to be susceptible to tree health problems such <br />as poor adaptation to site, air pollution, other elm pests or pathogens (such as elm yellows <br />or elm leaf beetle) or even other strains of OED which may eventually develop. Thus it is <br />prudent to plant a mixture of suitable cu1tivars of as many elm genotypes as possible. <br /> <br />Santamour and Bentz (1995) recently published a checklist and brief description of elm <br />cu1tivars in North America. The only true American elms on that list that are commercially <br />available and have strong evidence ofDED tolerance or resistance are the Princeton Elm, <br />the American Liberty "multi-clone," and Independence, which is one of the cultivars in the <br />American Liberty multi-clone. Two additional American elms, Valley Forge and New <br />Harmony, were released by the USDA National Arboretum since the Santamour and Bentz <br />listing was prepared. These two cultivars, which exhibit high tolerance to DED, should be <br />available through retail nurseries by 2001. <br /> <br />Besides true American elms, there are many other hybrid elm crosses and species of elm <br />that have high tolerance or resistance to OED. Several of these have attractive form, are <br />well suited to urban environments, and are readily available (figure 9). Many of these are <br />listed and described by Santamour and Bentz (1995) in the previously mentioned checklist. <br /> <br />http://www.na.fsJed.uslspfolpubslhowtoslht_dedlht_ded.htm <br /> <br />8/25/2004 <br /> <br />~- <br />