124 



Diseases of Economic Plants 



Ventilation and removal of shading trees are beneficial. 

 Close planting should be avoided in order to allow quick 

 drying, trelhses 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 

 sulfur. The sulfur, when the temperature is above 24° C. 

 (75° F.), passes into the air, and its fumes, coming in contact 



Fig. 63. 



Black-rot spots fiilargccl to show the pycnidia. 

 After Anderson. 



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

 sulfur is effective the fungus will make but Httle progress. 

 When the air, shade temperature, is from 32° to 35° C. (90° 

 to 95° F.), the killing effect of the sulfur may be seen within 

 24 hours; if above 38° C. (100° F.), one or two days are suf- 

 ficient to rid the vineyard of the disease. The sulfur must 

 be distributed to every part of the vine. Sulfur upon the 

 ground is of no use. The vines should be dusted from one to 

 seven times, according to conditions, susceptibility, climate, 

 etc. The first sulfuring should be done when the blossoms 



