Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 132 DISEASES OF ECONOMIC PLANTS probable, therefore, that at least one cause of crown gall is the organism mentioned. All diseased stock should be avoided, as well as stock from nurseries where the disease is known to exist. Bacteriose (Bacterium pruni E. F. Smith1).—A 'shot hole' disease of peach leaves, which causes prema- ture defoliation, is attributed by Smith and by Rorer 2 to bacteria. The disease has been found during several years in different states and is believed to constitute one of
Diseases of economic plants (1910) Diseases of economic plants diseasesofeconom02stev Year: 1910 132 DISEASES OF ECONOMIC PLANTS probable, therefore, that at least one cause of crown gall is the organism mentioned. All diseased stock should be avoided, as well as stock from nurseries where the disease is known to exist. Bacteriose (Bacterium pruni E. F. Smith1).—A 'shot hole' disease of peach leaves, which causes prema- ture defoliation, is attributed by Smith and by Rorer 2 to bacteria. The disease has been found during several years in different states and is believed to constitute one of the most common of the ' shot-hole ' dis- eases in the South and Middle West. The fruit and twigs are also affected. Upon the leaf it appears as somewhat angular purplish brown spots, 2-5 mm. FlG- 59.—Mildew upon in diameter, which may coalesce and in- peach fruit. After Volve large areas. Upon twigs it kills the bark, forming purplish black sunken areas, 2-3 mm. wide, which may extend to 3-8 cm. in length, and even girdle the twig and kill the shoot. Infection is most frequent at a leaf scar. Upon the fruit small pur- plish spots appear. Over these the skin soon cracks. The Elberta is especially susceptible. No effective treatment has yet been demonstrated. Powdery mildew, podosphaeriose (Podosphceria Oxycanthce (DC.) DeBy.). — This widespread mildew is in general ap- pearance very similar to the powdery mildew of the grape- cherry, lilac, and rose, etc. It sometimes becomes so abun- 1 Smith, E. F., Sci. n. s. 17, 456, and Bacteria in Relation to Plant Dis- ease, I, Figs. 11, 15, 70, 71, 72, and PI. 19. 2 Rorer, J. B., Mycologia 1, 23, January, 1909, and Sci. n. s. 30, 224.
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