. Carnegie Institution of Washington publication. ECONOMIC ASPECTS. 93 CONDITIONS FAVORING THE SPREAD OF THE DISEASE. The conditions favoring the spread of diseases may be wholly telluric, such as high temperature, unusual drought, cold weather, fogs, heavy dews, and excessive or continuous rainfall. These diseases may be favored by lack of natural drainage, or may be brought on by a variety of causes which are largely within the control of the grower, such as selection of improper varieties, i. e., very susceptible ones, overcultivation, storage at too high temperatures (in case of cabbage an
. Carnegie Institution of Washington publication. ECONOMIC ASPECTS. 93 CONDITIONS FAVORING THE SPREAD OF THE DISEASE. The conditions favoring the spread of diseases may be wholly telluric, such as high temperature, unusual drought, cold weather, fogs, heavy dews, and excessive or continuous rainfall. These diseases may be favored by lack of natural drainage, or may be brought on by a variety of causes which are largely within the control of the grower, such as selection of improper varieties, i. e., very susceptible ones, overcultivation, storage at too high temperatures (in case of cabbage and root crops), the use of infected soils, or manures, or seeds, or plants, and, especially in hot-houses, by the mismanagement of water and heat, and by the neglect to destroy the first diseased plants that appear and such transmitters of disease as insects and slugs, which frequently abound in Fig. 77.* METHODS OF PREVENTION. In case of certain diseases, copper fungicides have been found useful, e. g., in walnut bacteriosis and some of the leaf spots, but in general we know as yet very little about bactericidal treatments. In the early stages of an outbreak some of these diseases may be controlled by extirpation of the affected parts, or by the removal of whole plants as soon as they show signs. Also, if possible, the common carriers of infection should be eliminated. Finally, one should not forget that the substitution of resistant vari- eties for susceptible varieties is one of the most hopeful methods for disposing of certain of these vexatious diseases. Whenever any- thing specially noteworthy has been discov- ered in the way of treatment it will be mentioned under each particular 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 Carnegie Institution of Washington. Washington, Carne
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