. Bulletin. Natural history; Natural history. Diseases of Fruit Trees, 1922-1928 471 prevalence, the index being , and an even greater relative increase in twig-blight intensity, Avhich has an index of For 1924, the prevalence of pear blight was determined to be per cent, and the twig-blight intensity per cent. This shows a decided fall in prevalence from the previous year but a slight increase in intensity. The epidemic of 1925, as shown by our 13 observations, was milder than those of either 1923 or 1924, but more severe than that of 1922. Its prevalence was per
. Bulletin. Natural history; Natural history. Diseases of Fruit Trees, 1922-1928 471 prevalence, the index being , and an even greater relative increase in twig-blight intensity, Avhich has an index of For 1924, the prevalence of pear blight was determined to be per cent, and the twig-blight intensity per cent. This shows a decided fall in prevalence from the previous year but a slight increase in intensity. The epidemic of 1925, as shown by our 13 observations, was milder than those of either 1923 or 1924, but more severe than that of 1922. Its prevalence was per cent, and its intensity per cent. This. Fig. 18. Trends of prevalence and intensity of peae-blight. discussion See text for tendency to decrease Avas not maintained in 1926, however, for in that year 21 records representing 4,806 trees gave the high prevalence index of and a twig intensity index of In 1927 the epidemic was again mild, the prevalence of the dis- ease being only per cent, and its twig intensity per cent. This very sharp reduction in the severity of blight was continued into 1928, when the prevalence index reached the very low point of and the twig intensity index fell to The year-to-year trends of the prevalence and twig intensity phases of the pear blight epidemics are shown graphically in Figure 18. In. 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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