. Bulletin. Natural history; Natural history. Illinois Natural History Survey Bulletin Vol. 31, Art. 4 Dutch elm disease, except seven elms removed in 1967 because of ice damage, were not included in the total number of trees recorded in this study. How- ever, elms that became large enough to be seen from the street during the 29-year period were included. The appearance and spread of each disease were recorded, starting wdth the first two trees attacked by phloem necrosis in 1944. Dutch elm disease did not appear until 1951. Observations were made at irregular intervals during the growing sea
. Bulletin. Natural history; Natural history. Illinois Natural History Survey Bulletin Vol. 31, Art. 4 Dutch elm disease, except seven elms removed in 1967 because of ice damage, were not included in the total number of trees recorded in this study. How- ever, elms that became large enough to be seen from the street during the 29-year period were included. The appearance and spread of each disease were recorded, starting wdth the first two trees attacked by phloem necrosis in 1944. Dutch elm disease did not appear until 1951. Observations were made at irregular intervals during the growing season from 1944 through 1950 to determine the incidence and pattern of spread of phloem necrosis. Diseased trees were located by frequent scoutings. As many as 8-14 scoutings were made in a grow- ing season. After 1950, the authors made two surveys annually through 1972, one in June and one in September. However, in some years the first survey was not. Fig. 4.—Distribution of 16 Champaign-Urbana, Illinois, elms affected by phloem necrosis from 1944 through 1948 (dated according to year when symptoms appeared) and of 412. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Illinois. Natural History Survey Division. Urbana, State of Illinois, Dept. of Registration and Education, Natural History Survey Division
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