. Bulletin. Natural history; Natural history. May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease 100 90H 80 70 ^ 60. z u 50- " 40- 30- 20- 10- OH. • Phloem necrosis and Dutch elm disease Dutch elm disease — Phloem necrosis 1948 1956 1960 YEARS 1964 1968 Fig. 12.—Accumulated percentages of the original population of 14,103 elms lost each year to phloem necrosis and Dutch elm disease in Champaign-Urbana, Illinois, 1944-1972. original elm population. With less than 1 percent of the elms remaining after IS years, the annual loss became a few trees. Phloem necrosis killed 2,9
. Bulletin. Natural history; Natural history. May, 1974 Carter & Carter: Phloem Necrosis and Dutch Elm Disease 100 90H 80 70 ^ 60. z u 50- " 40- 30- 20- 10- OH. • Phloem necrosis and Dutch elm disease Dutch elm disease — Phloem necrosis 1948 1956 1960 YEARS 1964 1968 Fig. 12.—Accumulated percentages of the original population of 14,103 elms lost each year to phloem necrosis and Dutch elm disease in Champaign-Urbana, Illinois, 1944-1972. original elm population. With less than 1 percent of the elms remaining after IS years, the annual loss became a few trees. Phloem necrosis killed 2,994 elms during the 29-year period, 1944-1972, while Dutch elm disease killed 11,062 elms during the 22-year period, 1951- 1972. Although no elms showed symp- toms of Dutch elm disease in 1970 or 1971, five trees were killed by the dis- ease in 1972. Of the original popula- tion of 14,103 elms in 1944, all but 40 had been killed by the fall of 1972, a period of 29 years. TIME OF YEAR IN WHICH ELMS DIED FROM PHLOEM NECROSIS AND DUTCH ELM DISEASE Starting in 1951 two surveys were made annually to record the number of elms affected by phloem necrosis and by Dutch elm disease. The first survey was made in the early part of the growing season, usually in June. The second survey was made in the late part of the growing season, usually in September. These surveys are referred to as the June and September surveys. Each year data were obtained on the Table 9.—Elms showing disease symptoms in June and September surveys, Champaign- Urbana, Illinois, 1955-1961. Elms Having Phloem Elms Having Dutch Elm Total Diseased Standing Necrosis Sympt cms Disease Symptoms Dea June a Elms Year June September Total June September Total September Survey Survey Survey Survey Survey Survey 1955 40 81 121 1,059 746 1,805 1,926 86 133 1956 21 39 60 1,162 674 1,836 1,896 160 528 1957 44 324 368 1,159 957 2,116 2,484 255 520 1958 217 127 344 1,049 721 1,770 2,114 447 1,323 1959 58 90 148 1,116 688 1,804
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