244 Diseases of Econoinic Plants 



the injuries produced by Peronospora. Injuries produced by 

 cold weather, prolonged rains, insects, etc., undoubtedly 

 afford weak points where infection may begin. 



The best preventive measures are to follow general h}^- 

 gienic precautions, rake up and destroy all dead and diseased 

 leaves, keep the injuries from insects and other fungi at a 

 minimum, and rotate crops as frequently as possible. 



Minor Diseases 



Downy-mildew {Peronospora effusa (Grev.) Rl^h.). — 

 Gray to slightly violet, downy spots upon the lower sur- 

 faces of leaves, accompanied by pale yellow spots upon the 

 corresponding upper surfaces, indicate downy-mildew. The 

 disease in its habit and damage resembles that of the grape, 

 p. 122. Serious loss is reported from New Mexico and 

 Virginia. 



Leaf -blight {Phyllosticta chenopodii Sacc.) affects the 

 leaves, especially at their bases, producing spots which bear 

 minute pycnidia. Leaf-spot {Cercospora bcticola Sacc.) often 

 ruins crops by yellowing and dwarfing the plants, thus ren- 

 dering them worthless for market. Soft-rot {Bacillus carot- 

 ovorus) occurs on spinach in shipment. 



SQUASH. See p. 178. 



SUGAR CANE i''^ '^-^^ 



Red-rot {Colletoirichum). — The first external evidences of 

 disease are drooping, withering, and yellowing of the upper 

 leaves, followed by wilting of the entire crown. Finally, the 

 whole stool dies. In less severe cases buds die, and dead, 

 black areas extend out from the nodes. The veins running 

 lengthwise within the stems are reddened. Uncertainty 

 exists as to identity of the causal fungus. The disease is 

 one of the most serious affecting sugar-cane. Only healthy 

 stock should be used in propagation, and diseased refuse 

 should be destroved. 



