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 ; 

 (6) 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 ; (/) 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) ; in some 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 : 



