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oe viewed only as an aid. Sanitation - removal of dead and dying elms - is the key to Dutch elm disease management. DETECTION METHODS Ground Survey Ground survey crews, able to work in most weather conditions, will detect a high percentage of the disease trees, which can be marked for removal. These crews shouid be able to recognize early symptoms of Dutch elm disease and understand how it is spread. They can observe more of the elm crown if the area to be examined is approached from several different directions rather than following the same pattern on each survey. Weekly surveys during June, July, and early August will detect most diseased trees. Ground surveys are slow and difficult in wild or undeveloped areas. Early infections evident only in the treetops can be missed from below. Ground survey by community residents may be effective as long as there is coordination and leadership. Experience Indicates communities cannot depend on every neighbor- hood to be as effective, efficient, and accurate as is required. Aerial Survey Aerial photography resuits in detection of 50-70 percent of the diseased trees. Advantages of this technique are the speed and iowcost ofthe operation. The lack of accuracy, weather limitations on flying time, problems in mapping locations of diseased trees, and dependence on ground crews to mark trees for removal are disadvantages. Aerial inspection after infected trees have been removed from an area is a good followup method and may detect additional diseased trees. While aerial photographY lacks the accuracy of a ground survey, it does provide an accurate up-to- date map of diseased trees and information on total tree populations. Aerial photography can be done quickly, If weather is suitable and aircraft available. The complexity of aerial photography requires a specialist to insure maximum resutts. Ektachrome infrared film with a Wratten 12 or21 filter at a scale of 1 :9600 is recommended. Various cameras are available for aerial photography and, atthough 9-inch is excellent, 70 mm or even 35 mm are suitable. Aerial photography will be of most value to the community if done in early July when trees are wilting and color contrasts are at a maximum. A second survey should be completed before August 15 to avoid fall coloration or discoloration of foliage due to other causes. PROSPECTS FOR MANAGEMENT IN MINNESOTA Excessively cold winters and highly fiuctuating spring temperatures may assist in managing Dutch elm disease. An effective sanitation program, however, is absolutely necessary to reduce elm losses. What your area or neighborhood does greatly determines the future of elms in the control zone. The movement of disease from wild areas outside the neighborhood into control areas is hard to manage and will eventually reduce the population of trees along the common border. But that should not deter efforts to manage the disease within the control zone, since most Dutch elm disease In Minnesota occurs from sources within a control area rather than from outlying wild areas. Wild areas should not be given high priority until the disease In the control zone has been successfully managed. Resistant Elms All species of elm are more or less susceptible to Dutch elm disease. Individual trees, especially in the Chinese and Siberian elm group, have some resistance but are not immune. Despite the resistance of Siberian elm, thespec;es is not recommended because it issubjecttowinterinjury and can support bark beetle populations. The resistant elms which have been developed do not have the size or growth form of the American elm. The best atternative isto plant a variety oftreespecies, other than elm, to avoid future disasters such as Dutch elm disease. 9