Dutch elm disease resistant elm cultivars
The American elm was at one time the most extensively planted shade tree in the United States because it was easily transported, fast growing, tolerant of limb and root pruning, tolerant of soil compaction, and had an elegant vase shape that made a perfect high canopy over city streets. In l920, Dutch elm disease fungus was first isolated in the Netherlands. In l930, it was reported in Ohio, several years later it caused a serious outbreak in the Midwest. It was first recorded in Minnesota in l96l. In the last 40 years, so many of our State's elms have died from DED that people considered it useless to replant elms, but research that began in l938 has resulted in several resistant American and Asian hybrids derived by crossing different elm species. Even so, it is a good idea to keep in mind that all these elms may be subject to health problems of sort or another (other diseases, insect defoliation, or environmental injury). Selecting DED resistant elms hardy for the location and planting them more that 50 feet away from other elms will prevent DED from being spread through root grafts.
If your are considering planting elms talk with your nursery about available elm cultivars that are DED resistant, hardy for your site, have your desired canopy shape and height, and turn to your preferred leaf color in the fall. Also ask about resistance (tolerance) or susceptibility to other diseases or insects such as leaf beetles or leaf miners. A l999 publication entitled Dutch Elm Disease and disease Resistant Elms has many colored pictures and sections dealing with symptoms, causal agents, disease transmission, control strategies, disrupting root grafts, fungicide injections, and disease resistant elms. It is available from Iowa State University Extension Distribution Center, ll9 Printing and Publications Building, Ames Iowa 50011-3171, telephone 515-294-5247, $1.50 each.