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How to Identify and Manage Dutch Elm Disease Page 13 of 16 Figure 9. Cultivars of elm selected for resistance to DED are available. This selection of Ulmu. japonica demonstrates the potential these elms have as landscape trees. (photo courteay of Dr. Eugene Smalley, University ofWi.consin-Madi.on} In addition to careful selection of the tree species and cultivar, location and spacing are also important to reduce losses from OED. When selecting landscape trees and their locations, plant a mixture of tree species appropriate to the site. In addition to the species diversity, consider spacing of the trees. Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity. Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and OED fungus to infect high value landscape trees. Management is necessary in order to protect urban elms. The most effective management option to reduce both the bark beetle vectors and the OEO fungus is sanitation to promptly remove stressed, dead and dying elms as previously described. However, this intensity of treatment is often not feasible. A "trap tree" method was developed in the 1980's to more cost effectively reduce populations of elm bark beetles. Under this method, OED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark. The bark beetles are attracted to the dying trees, but the rapidly drying bark is unsuitable for them to complete their lifecycle, and the bark beetle populations are reduced. However, treated trees may then become hazard trees with high risk offalling and causing http://www.na.fs.fed.us/spfo/pubs/howtos/ht_ded/ht_ded.htm 8/25/2004