GRAPE PESTS 17 



raised black pustules. These pustules are the spore bodies of the fungus. The 

 fungus over-winters in the shriveled berries and the infected parts of the vine. 



Downy Mildew — Plasmopara viiicola (B. & C.) Berl. & DeToni 



Downy mildew develops on all green parts of the vine and on the berries. 

 On the leaves this disease forms yellowish spots which turn reddish brown on the 

 upper surface and eventually die out. A glistening loose white cottony or frost- 

 like giowth develops on the lower surface of the leaves. When the disease is 

 severe, the infected leaves and shoots are dwarfed, dry up, become brittle, and 

 fall. Infected berries at first show brownish-purple spots, become hard, and are 

 covered with the cottony or downy fungus similar to that on the leaves. They 

 rot, turn brown, w'ther, and fall. The fungus hibernates in diseased leaves. 



Powdery Mildew — Uncinula necator (Schw.) Burr. 



This disease appears at first as pale greenish mottled patches on the leaves, 

 the surfaces of which are covered with a white or grayish powdery mildew. This 

 growth is composed of summer spores which spread arid continue the infection 

 throughout the growing season. Badly infected foliage has a musty, moldy odor. 

 Patches of mildew also appear on the new shoots, stems of the fruit clusters and 

 stalks of the individual berries. The infected berries have a gray scurfy appear- 

 ance and are dwarfed or grow irregularly. In severe cases they may crack open, 

 fail to mature, and drop. Numerous minute black pustules or spore bodies 

 carry the disease over winter on the infected parts of the vine. 



Control of iVIore Important Grape Diseases 



Black rot, downy mildew, and powdery mildew thrive and cause serious damage 

 only with continuous or excessively moist weather and are control'ed by the 

 same treatment. 



Vines growing in locations which receive normal sunshine and have good air 

 drainage ordinarily require very little protection with fungicides. If planted in 

 depressions or shaded by trees or buildings, the vines may need the protection of 

 two or more applications of bordeaux mixture or copper dust as indicated in the 

 accompanying Spray Schedule. 



Infection of new growth takes place in wet weather from spores which issue 

 from the infected parts of the vine which have over-wintered on the ground or 

 on the trellis. Careful pruning by a recommended system and the destruction 

 of the cut canes and fallen leaves will eliminate many sources of infection and 

 prevent a dense growth of foliage which interferes with drying. During the grow- 

 ing season tall grass and weeds should be cut close to the ground to aid the cir- 

 culation of air. 



On a few vines, choice bunches of grapes can be protected from diseases as well 

 as from insects and birds by enclosing them in a paper bag soon after the berries 

 form. Howe\'er, it may be necessary to protect the fob'age by spraying. 



