Insect and Fungous Enemies of the Grape. 51 
Covering the bunches of grapes with paper bags soon after the 
blossoms fall is usually an effective means of preventing black-rot 
and most other fungous diseases of the fruit. It is generally re- 
garded as too laborious and expensive a method for large vineyards, 
but may be profitably practiced where only a small number of vines 
are grown or where special market conditions or prices make it 
advisable. 
Fig. 56.—A, An average bunch of grapes, showing the proportion of rotten berries 
(90.7 per cent), in an unsprayed plat. B, An average bunch of grapes, showing 
the proportion of rotten berries (4.3 per cent) in a sprayed plat in the same 
vineyard. Three-fourths natural size. 
DOWNY MILDEW. 
Downy mildew * in certain seasons and in northern localities some- 
times causes more loss than black-rot and is a close rival for first place 
among the fungous enemies of the grape. It attacks all the tender, 
growing parts of the vine. Usually it is at first most noticeable on 
the foliage, producing greenish yellow, irregular spots upon the 
upper surface, which become reddish brown. At the same time there 
appears on the under surface of the leaf, a thin, loose, white, downy 
growth, suggestive of hoarfrost (fig. 57). This growth consists of 
the fertile fungous filaments bearing the summer spores (fig. 58, a, 6), 
which, under favorable conditions, are distributed by wind and water 
to the berries and other parts, where they germinate and produce zoo- 
® Caused by Plasmopara viticola (B, & C.) Berl, & De Toni, 
