314 



STATE HORTICULTURAL SOCIETY. 



POWDERY MILDEW OF THE GRAPE (Uncinula ampelopsidis) . 



The so-called pow- 

 dery mildew is partic- 

 ularly troublesome in 

 seasons when it is hot 

 and dry, and it attacks 

 the foliage and young 

 shoots as well as the 

 fruit. It is particular- 

 ly troublesome to the 

 varieties that are hy- 

 brids of Vitis vinifera, 

 the European wine 

 grape. The fungus 

 lives upon the surface 

 of the leaves and ob- 

 tains its food by send- 

 ing root-like suckers 

 called haustoria, into 

 the underlying cells, 

 from which they ab- 

 sorb the contents. The 

 summer spores are 

 borne upon simple 

 spore stalks ( Fig. 29, 1 ) 

 and serve for the rapid 

 reproduction of the 

 fungus. The formation 

 of the winter spores is 

 illustrated in Fig. 29, 4. 

 The spore cases of the 

 grape powdery mildew 

 can be readily distin- 

 guished from others 

 by having the extremities of their appendages arranged in coils. 



The thick covering of the winter spores {perithecia) serves to protect 

 them from extremes of temperature and moisture during the winter. 



The affected portions, during the first half of the season, take on a 

 whitish, powdery appearance, which, later on, changes to a light brown, 

 owing to the presence of great numbers of winter spores. As both the 

 spores and the body of the fungus are upon the surface of the leaves, it is 

 easy to destroy them wherever the copper compounds can be brought into 

 contact with them, but, as it often appears inside the fruit clusters, it is diffi- 

 cult to exterminate if it once gets a start. The sprayings with Bordeaux 

 mixture, that are generally applied for the other diseases, will do much to 

 hold it in check, during the early part of the season, but, later on, as the 

 fruit approaches maturity, the weak copper sulphate or the ammoniacal 

 carbonate of copper will be preferable. The application of flowers of 

 sulphur to such varieties as are subject to this disease, at intervals during 

 the season, will also be of value, especially on grapes grown under glass. 



In dry seasons the frequent stirring of the soil will aid in keeping the 

 vines healthy, but upon its first appearance, recourse should be had to one 

 of the above fungicides. 



Fig. 29.— Powdery Mildews of Rose, Cherry, and Grape. 7, sammer spore 

 of rose mildew; 2-4, development of carpogoninm; 5, winter spore 

 {perithecium) with ascns, containing ascospores escaping; ti, aammer 

 spores of cherry powdery mildews; 7, winter spore of same ; 10, myce- 

 lium with haustoria in cells; 11, 12, 13, the same, of the powdery mildew 

 of the grape. — After De Bary. . 



