SMALL FRUITS 165 



is mildewed soon ceases growth and falls, or develops ir- 

 regularly and fails to ripen. 



The mildew fungus is strictlj^ superficial and may be 

 easily rubbed off, leaving a discolored spot. In late stages 

 perithecia may be recognized as very small black bodies, about 

 0.1-€.12 mm. in diameter, lying within the diseased areas. 

 The disease develops in most destructive form in shaded, 

 damp, poorly ventilated situations. Rain and fogs favor 

 it, while very dry weather inhibits it. The American vines 

 are less susceptible than the European varieties. 



Ventilation and removal of shading trees are beneficial. 

 Close planting should be avoided in order to allow quick 

 drying, and trellises should run in such direction as to allow 

 free access of sun. But these means are only palliative. 



To control the. mildew in dry climates employ flowers of 

 sulphur. The sulphur, when the temperature is above 75 ° 

 F., passes into the air, and its fumes, coming in contact with 

 the fungus, kill it. Below the temperature at which sulphur 

 is effective the fungus will make but little progress. When 

 the air, shade temperature, is from 90° to 95° F., the killing 

 effect of the sulphur may be seen within 24 hours ^ ; if above 

 100°, one or two days are sufficient to rid the vineyard of the 

 disease. The sulphur must be distributed to every part of 

 the vine. Sulphur upon the ground is of no use. The vines 

 should be sulphured from one to seven times, according to 

 conditions, susceptibility, climate, etc. The first sulphur- 

 ing should be done when the blossoms begin to open; a 

 second application should be made before the first sign of 

 the mildew, and other applications should follow as need in- 

 dicates. It is necessary to resulphur if from one to two days 



1 Bioletti, F. T., Cal. Agr. Exp. Sta. Bui. 186, February, 1907. 



