GRAPE DISEASES 247 
it can withstand more drought than other grape fungi. Hence 
anything which permits sun and air to reach all parts of the 
vine may lessen the danger from mildew: (a) remove rows of 
trees which shade the vines on the south side; it is assumed 
that this will be done only in the case of trees of small worth; 
(b) plant vines at a reasonable distance apart so that they may 
~ dry off more quickly after dews, fogs and rains; (c) rows which 
extend north and south are said to evaporate their moisture 
most easily ; this should be borne in mind when planting grapes 
in mildew-regions; (d) likewise, low-trellised vines are more 
easily dried by the sun and wind; (e) wet places should be 
drained ; (f) vines should be pruned so that they will spread ; 
this is of value in the moisture consideration. 
The fungus may be eradicated from the vines by the use of 
sulfur dust (powdered sulfur, or flowers of sulfur) ; insome regions 
this may be done cheaply and effectively. Old and young 
vines alike should be dusted. The sulfur acts by killing the 
mycelium of the fungus which, it will be remembered, is super- 
ficial. Fortunately the sulfur acts at temperatures which are 
optimum for the fungus, the rate of the killing increasing as 
the temperature rises from 75° to 100° Fahr. So far as possible, 
dusting should be avoided when the vines are very wet. Ap- 
plications of dust to the soil have been shown to have practi- 
cally no effect on powdery-mildew. In California injury from 
the use of sulfur may be expected only when the temperature 
is above 110° Fahr. and only on varieties like the Isabella, 
Othello and other American varieties. In the Chautauqua 
belt of New York sulfur dust causes considerable injury and 
should not be used except on vines of European origin. It 
has been noticed that sulfur-dusted grapes show less tendency 
to drop their blossoms, and also ripen their fruit seven to ten 
days earlier than vines not so treated. 
One to six applications of sulfur are necessary, depending on 
the locality, weather, variety and exposure. Apply as follows: 
