504 INSECTS AFFECTING VEGETATION 



of disease in the cutting is proportionate to the degree or stage of the 

 disease in the parent vine. Cuttings from diseased vines may root 

 well and produce a fine, healthy-looking top, especially in the 

 spring, but as the heat of the season approaches these young vines 

 show disease, dying earlier or later, according to the length of time 

 the parent vine has been affected. The disease is also found to be 

 cumulative in its action. The longer the vine lives the more obvious 

 becomes its unhealthy condition, the vitality of the plant being 

 gradually overcome. 



When the disease was most virulent it was learned that vines 

 grown from healthy cuttings procured from outside of infected dis- 

 tricts would also contract the malady and die. As time passed, how- 

 ever, it lost much of this virulence, and the setting of healthy cut- 

 tings can now be recommended with more confidence than formerly. 

 Numerous vineyards are growing and bearing well which were 

 started from healthy vines, while the disease is still apparent in 

 many vineyards set from cuttings procured within the infected dis- 

 trict. 



Powdery Mildew. This is one of the most common fungous 

 diseases of the vine. It is present in nearly all the grape-growing 

 countries of the world, but is most destructive in warm and humid 

 localities; for instance, near the sea. In California it was known as 

 early as 1860 or 1861, and is now present in most of the vineyards 

 along the coast. This fungus grows on the canes, the leaves, and the 

 fruit; its greatest injury, however, is done to the latter, as it checks 

 the growth of the berry, either entirely or on one side, the parts af- 

 fected becoming hard. When one side only is attacked the further 

 growth of the berry causes the dried surface to burst open, wholly 

 destroying the fruit. 



Powdery mildew has two kinds of reproductive bodies or 

 spores, one for rapid summer distribution and the other to preserve 

 the fungus over winter. In the warmer portions of the Pacific coast 

 the summer spores are the only ones commonly observed. When 

 abundant they give a whitish, powdery appearance to the parts of 

 the host affected, and it is from this appearance the fungus derives 

 its name. These white summer spores are called conidia. The 

 winter fruits are produced on the approach of cold weather, and, 

 unlike those of summer, are thick-walled, blackish bodies, securely 

 inclosing and protecting the delicate spores. They are more or less 

 abundant according to the climate where the vine is grown. 



This disease can be easily treated, owing to the fact that the 

 vital portions of the fungus grow upon the surface, making possible 

 the use of remedies as well as preventives. 



Erinose of Grape. Erinose is a disease of the vine character- 

 ized by swellings on the upper surface of the leaves, and correspond- 

 ing depressions on the lower surface. These swellings, when num- 

 erous, cause considerable deformation of the leaves, but not the 

 change of color to yellow or brown which is characteristic of most 

 fungous diseases. Even very badly-affected leaves retain almost 

 their normal green color until late in the season. The depressions 



