1G6 DISEASES OF ECONOMIC PLANTS 



at 90° to 95° or four to five days 85° to 90° do not in- 

 tervene before the sulphur is removed by rain. If the 

 disease was bad the previous, year, it is well to sulphur 

 even earlier than indicated above, i.e., when the shoots 

 are about 15-20 cm. long. 



After the grapes commence to ripen they are nearly safe 

 from mildew, but for the future good of the vine the leaves 

 should be protected by further sulphuring if need be. 

 Young vines should similarly be protected. To properly 

 sulphur use good dust sprayers which give an even flow 

 of sulphur and are easy of operation. The cost of sulphur- 

 ing an acre three times is about $1.25. 



In climates where sulphur cannot be used to advantage 

 reliance must be placed upon Bordeaux mixture applied as 

 for the black rot. 



Downy mildew, brown rot, gray rot (Plasmopara viticola 

 (Berk. & Curt.) Berl. & De Toni). — Each of the downy 

 mildews produces a more or less distinctly visible downy 

 or velvety growth upon the affected surface. This ap- 

 pearance is caused by myriads of spore-bearing stalks 

 that rise from the diseased surface. If these stalks are 

 close together, the appearance is thoroughly character- 

 istic and the diagnosis clear. As the spores mature the 

 spots assume a gray or frosted appearance. 



The European are more susceptible to this mildew than 

 the American varieties. All the green parts of the plant 

 are affected. Upon the lower side of the leaf the disease 

 may be recognized by the description given above. The 

 upper surface of the leaf over a diseased spot becomes 

 pale, yellowish, and finally turns brown and dies. The 

 area so affected is definitely bordered and does not nee- 



