. Bulletin. Natural history; Natural history. 458 Illinois Natural History Survey Bulletin course, be determined. The result of the movement of the known pre- valence indexes was, nevertheless, to bring about a rise in the disease incidence curve to approximately the height of 1923. In lf)2(). three diseases fell olf in prevalence, scab very sharply, blotch quite sharply also, and fire-blight only slightly, while of the other two diseases, black-rot increased somewhat in prevalence and rust rose to the highest point recorded up to that time. 'The net result of these changes was to drop the dis
. Bulletin. Natural history; Natural history. 458 Illinois Natural History Survey Bulletin course, be determined. The result of the movement of the known pre- valence indexes was, nevertheless, to bring about a rise in the disease incidence curve to approximately the height of 1923. In lf)2(). three diseases fell olf in prevalence, scab very sharply, blotch quite sharply also, and fire-blight only slightly, while of the other two diseases, black-rot increased somewhat in prevalence and rust rose to the highest point recorded up to that time. 'The net result of these changes was to drop the disease incidence curve to a point only slightly higher than it occupied in 1922. ^o. SCOA B/of-e/i Black-r of Firt B''i^t^â /o /32Z 23 '24 '25 '26 '27 'Z8 Fig. 11. Comparison of the prevalence trends of apple diseases and of THE average incidence OF DISEASE PER TREE. SeE TEXT FOR DISCUSSION The general retrogression of disease prevalence in 1926 was com- pensated during the 1927 season by a rise in prevalence of all diseases except fire-blight, which fell to its lowest point in our series of records, and the result was to raise the disease incidence curve to the highest point recorded up to that time. This general increase was continued into 1928. Fire-blight rose very sharply to a high degree of prevalence, black-rot, rust, and scab maintained or increased their former high indexes, and blotch alone de- creased, with the net result that the average incidence of diseases per tree rose, as the upper curve shows, to the high point of 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
Size: 1688px × 1479px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., booka, bookcentury1900, bookdecade1910, booksubjectnaturalhistory
