EXPERIMENT STATION BULLETINS. 313 



This important fruit seems to be particularly subject to the attack of 

 various fungous diseases and all parts of the plant, including stems, leaves, 

 and fruit, are often so seriously injured that the crop of fruit, is lost and the 

 strength of the plant greatly impaired. 



It is all the worse because they come at various times and under differ- 

 ent conditions. Thus the downy mildew is favored by cold, wet weather, 

 while the so-called powdery mildew luxuriates when it is hot and dry. 



This disease, which is sometimes called the American vine disease, is 

 often quite troublesome to the foliage and fruit of our grapes. The spores 

 from which it develops fall upon a leaf and in the presence of moisture 

 quickly germinate. The germinating tube gains entrance through the ' 

 breathing pores to the interior of the leaves and, passing between the cells 

 of which they are composed, sends its root-like haustoria through the cell- 

 walls (Fig. 28, 14) and absorbs the cell contents, to be used in its own 

 development. This destruction of the cells causes brown or yellow spots 

 to appear, after which the leaves turn yellow and finally brown, and this is 

 the first indication that will be noticed of the presence of the disease. 



If the conditions are favorable, the stalks upon which the spores are 

 developed will push through the stomata on the under side of the leaves 

 and ripen an immense number of oval, colorless, summer spores or conidia. 

 (Fig. 28, 1 and 2). The stalks and the spores together show as downy or 

 frosty patches, generally on the under side of the leaves, although they 

 may, if the attack is a severe one, appear on the upper side as well as on 

 the leaf petioles and young branches. 



The growth of the fungus and the development of the spores are well 

 illustrated in Fig. 28. The leaf soon shrivels as seen at Fig. 28, 3, and, later 

 on, the thick-walled winter cells form within the leaves. Within them they 

 fall to the ground and are ready to spread the disease the following year. 

 While this disease may attack almost any variety, it is most likely to 

 appear upon such kinds as are naturally weak, or that have become so 

 through soil exhaustion, from over-bearing, or from the attacks of insects 

 or fungi. 



The fungus checks the growth of the berries and causes them to turn 

 brown, so that the disease has often been termed brown-rot. When the 

 spores are developed upon the berries it gives them a grayish, mealy 

 appearance. The disease is particularly troublesome in cold, wet seasons 

 when the plants have been weakened by the unfavorable conditions under 

 which they have been growing. 



As in nearly all other cases, a fungicide, to be efficient against this dis- 

 ease, should be applied before the spores have germinated upon the plants. 

 This will necessitate an application early in the spring before the buds have 

 swollen, for which spraying copper sulphate solution can be used, and it 

 should be applied thoroughly to all parts of the vines, the trellis, and the 

 soil beneath. In this way great numbers of spores can be destroyed. A 

 second application, using Bordeaux mixture, should be made when the first 

 leaves are about one half grown, and this should be repeated as soon as the 

 fruit has set. The later applications should be made at intervals of from 

 ten to fifteen days according to the weather and the prevalence of the dis- 

 ease. If the summer is cool and wet, as many as five or six applications can 

 be made with profit, and although when the disease is very prevalent the 

 foliage and fruit may not be entirely protected, yet the injury will be very 

 slight, while, were no use of the fungicide whatever made, the entire crop 

 might have been lost. 

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