29 



likely to suffer so severely from most diseases as those which are 

 neglected. 



The principal fimgoiis diseases in the order of their importance are 

 black-rot, downy mildew, powdery mildew, anthracnose, and ripe-rot. 

 There are also other diseases, which will be referred to later, but they 

 are either not of sufficient importance to deserve much attention here 

 or else their treatment is not yet satisfactorily determined. 



BLACK-ROT. 



Black-rot is the most generally distributed and destructive fimgous 

 disease of the grape in the region east of the Rocky Mountains. It 

 is caused by a parasitic fungus known as Guignardia hidwellii (Ell.) 

 V. & R. It gains entrance to the plant by means of minute germs 

 called spores. These are borne in small black spore cases, and can 



Fig. 10. — The black-rot fungus {Guignardia bidwellii): a, A portion of an affected grape, showing the 

 pustules in which the spores are produced (slightly magnified); 6 a section of one of these pustules 

 very highly magnified, showing the manner In which the summer spores are produced and dis- 

 charged; c, a sac containing winter spores; d, single winter spores very highly magnified. 



not be seen with the naked eye. They are distributed chiefly by the 

 wind and rain. Two or more forms of spores are produced, as shown 

 in the accompanying illustration (fig. 10, 6). When these spores 

 come in contact with the young and tender parts of the vine, under 

 favorable conditions, they germinate and produce a slender tube, 

 which penetrates the tissue and may destroy it. 



This disease attacks the leaves and shoots, as well as the fruit. It 

 usually makes its first appearance on the leaves and young shoots, 

 producing reddish-brown dead spots. The fruit may be attacked 

 when young, but usually the disease does not attract attention until 

 the berries are half grown or more. Brown or blackish spots first 

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