An Urban Epiphytotic of Phloem Necrosis and Dutch Elm Disease, 1944-1972

Abstract

THE AMERICAN ELM was used more extensively than any other species as a shade tree in Illinois prior to 1940. It was especially valued for its rapid growth, majestic size, vase shape, and extensive shade. It was used for streets, boulevards, and park drives, as well as in lawns. In many cities throughout the state it represented half or more of the shade trees lining the streets. In some cities it was estimated that three-fourths of the shade trees were American elms. Because of the loss to diseases of millions of elms, especially American elms, since 1940, most cities and homeowners now plant other trees. The elm problem has made many people aware of the importance of using diversified plantings to avoid such a catastrophe in the future. Extensive dying of elms in central Illinois, especially in Bloomington, Normal, and Champaign, occurred as early as 1883 (Forbes 1885:112; 1912:3). This dying of elms subsided within a few years. Although the cause of the elm deaths was not determined, the symptoms reported are not typical of any current vascular wilt disease. The present study was initiated, following the appearance of phloem necrosis in Urbana in 1944, to obtain data on the number of elms affected annually by the disease and to study the pattern of spread in a municipal area where no city-wide control program was practiced. With the appearance of Dutch elm disease in Urbana in 1951, the study was expanded to include both diseases and the relationship of the two diseases in a municipal area.