Family Convolvulaceae 165 



protruding. The fungus, so far as is known, lives 

 only on sweet potato foliage. 



SEPTORIA LEAF SPOT 

 Caused by Septoria bataticola Taub. 



Leaf spot is a disease which is of little economic 

 importance. The trouble appears as soon as the 

 plants attain full growth and are beginning to 

 lose in vigor. The disease has been found in New 

 Jersey, Delaware, Maryland, Virginia, Iowa, and 

 other States. 



Symptoms. Leaf spot is characterized by small 

 whitish spots scattered indiscriminately over the 

 leaf. The spots are nearly always surrounded by 

 a brown border (fig. 27 b). On the surface of the 

 dead tissue are found the pycnidia which are usually 

 few in numbers, often not more than one or two to a 

 spot. The pycnospores are carried about from leaf 

 to leaf by winds or insects. 



Septoria bataticola attacks only sweet potato foliage. 

 It is very likely that the fungus hibernates on the 

 dead leaves in the field. Leaf spot is never serious 

 enough to warrant special methods of control. 



JAVA BLACK ROT 

 Caused by Diplodia tubericola (E. and E.) Taub. 



The disease was first found on some sweet potatoes 

 that were brought to the Louisiana station from 

 Java in the spring of 1894. The potatoes appeared 



