Vegetable and Field Crops 



159 



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Minor diseases 



Orobanche is sometimes parasitic on beans. Sunscald ^^^ 

 produces discoloration. Powdery-mildew (Erysiphe polygoni 

 DC.) often gives a rusty color to the pods. Leaf-blotch 

 (Cercospora cruenta Sacc.) occurs only upon the foliage as 

 brownish patches, causing the ^ 



leaves to fall away. The spots ^^^'^ 



are large, angular, and limited ^^, ^ 



by the veins. Leaf-spot (Isar- / 



iopsis griseola Sacc.) is chiefly 

 limited to the foliage, produc- 

 ing small, angular spots, over 

 the under surface of which the 

 fungus forms a gray, moldy 

 covering. It has been ob- . ^L 

 served in many states, and is "-'*'' 

 most injurious in the South. ^'^' 

 Wilt due to Pseudomonas sol- 

 anacearum has also been re- 

 ported. Root-knot (nema- 

 todes) is injurious in some 

 localities. Streak. — Dark 

 spots occur on stems, leaves, 

 and pods. The cause is un- 

 known. Mosaic ^^ in general 



character resembles tobacco j,^^ gg _ j^i,^^.^^^^ p^^^ ^l^^^. 

 mosaic. It appears to be of ing pod-blight. After Halsted. 

 wide distribution and to be 



communicated through the seed. Resistant strains should 

 be grown. 



BEET, CHARD, MANGOLD, MANGELS 



Cercospora Leaf-spot ^^^~^^'' {Cercospora beticola Sacc). ^ 

 This, one of the several leaf-spots upon the beet, is very 

 widespread in the eastern and middle states. Very few 

 fields are entirely free from it. It occurs upon all varieties, 

 but is especially injurious to the sugar beet. 



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