Diseases. 



GRAPE MANUAL. 



Treatment. 55 



berries rotting from the attacks of this fungus 

 and yet showing no external evidence of the 

 parasite. Bro^^n rot is the name usually 

 given to this form of the disease. Berries 

 affected with brown rot show at first small, 

 purplish brown spots. Soon the entire berry 

 turns brown, and the pulp becomes soft and 

 often shriuks, forming depressions, over which 

 the wrinkled but otherwise smooth and un- 

 broken skin is stretched (Fig. 78). 



Powdery Milclew.* — Powdery mildew at- 

 tacks the leaves, young shoots, and berries, 

 covering the same with a whitish, cobweb-like 

 growth. This disease is also widely distrib- 

 uted, being especiallj^ troublesome on the 

 Vinifera grapes of the Pacific coast and Eu- 

 rope, and causing what is generally known as 

 the Grape-vine Oidium. Leaves affected with 

 the fungus show usually upon the upper sur- 

 face a whitish, web-like, powdery growth, 

 which is not restricted by anything like a 

 definite border. The fruit shows a similar 

 growth on the surface, but eventuall}'', as a 

 result of the attack of the parasite, the skin 

 of the berries cracks, admitting other agents 

 of decay, which soon finish the work of de- 

 struction. 



Anthraoiose.f — This disease has of late 

 years attracted considerable attention in this 

 country, where it occurs on the leaves, young 

 shoots, and fruit. It prevails also in Europe, 

 but has never proved as serious there as the 

 downy and powdery mildews. 



Leaves when first affected with this dis- 

 ease show minute blackish-brown spots, 

 which are surrounded with a slightly raised 

 ■darker-colored margin. Ultimately the cen- 

 ter of the spots turns gray, and not infre- 

 quently the diseased parts separate from the 

 surrounding healthy portions, leaving the leaf 

 full of small, ragged-edged holes. On the 

 shoots the disease manifests itself in much 

 the yame way as it does on the leaves. As it 

 progresses, however, the spots usually retain 

 their dark color and often run together, form- 

 ing more or less elongated diseased areas, 

 which gradually eat their way into the wood, 

 and it is now known that the mycelium, or 

 bod}^ of the fungus, passes the winter in the 

 tissues surrounding these places. 



Anthracnose on the fruit, or bird's-ej^e rot, 

 as it is sometimes called, first appears as a 

 black or brownish circular spot, surrounded 

 by a narrow, somewhat darker rim. As the 

 spots increase in size the color undergoes 

 various changes. In some cases the outside 

 rim remains dark brown, while inside of this 

 is a wider zone of a beautiful vermilion color, 



* Unciuula spiralis Berk. 



+ Spaceloina aniplinum l)e Bary. 



Fig. 79.— Anthracnose. 



surrounding a grayish- white center (Fig. 79). 

 Frequently the spots, when less than one- 

 eighth of an inch in diameter, assume a gray- 

 ish-white color, which they retain throughout 

 the rest of their growth. When the berries 

 are small the disease often manifests itself in 

 another way. The fruit turns brown and 

 shrivels up, and at the same time little pinkish 

 pustules appear on the surface. 



This form of rot is not characterized by a 

 softening of the tissues, as is the case with 

 others we have mentioned. The tissues slowly 

 collapse, at the same time becoming hard 

 and leathery. 



METHODS OF COMBATING THE DISEASES. 



With the exception of Anthracnose, all 

 the diseases described in the foregoing pages 

 may in large part be successfully combated 

 by applying, at the proper time, either in the 

 form of a liquid or powder, certain substances 

 known as funs>icides. The fungicides do not 

 injure the young and tender parts of the vine, 

 but they do destroy or prevent the develop- 

 ment of the parasitic organisms which bring 

 about the diseases described. The applica- 

 tion of a fungicide, therefore, acts, to a cer- 

 tain extent, as a shield to the various parts of 

 the grape, protecting them from infection in 

 much the same way that a glass jar or paper 

 bag would ])rotect. It will be seen from what 

 has been said that the treatments are largely 

 preventive, not curative, hence the import- 

 ance of doing everything at the proper time, 



