164 The Sweet Potato 



to scatter to other sections of the leaves. This disease is 

 not known on other host plants and only on the leaves 

 of the sweet potato plant. It prohably winters on the 

 dead leaves, and may be transmitted by insects, wind, 

 or rain. 



Leaf-spot is widely distributed, having been collected 

 from the eastern coast and also from the states of 

 Iowa and Illinois. This disease has never been known 

 to be serious; no remedies are required. 



WHITE-EUST (leaf-mold) 



{Albugo ipomcecB-pandurance) 



The first symptom of white-rust is a loss of the green 

 color in the indefinite spots on the under side of the 

 leaf. (Plate VIII.) Later these spots become brown 

 and covered with a whitish viscid growth, which is fi- 

 nally more or less powdery. This white powdery mass 

 is made up of numerous spores or reproductive bodies, 

 which serve to start a new infection if they fall on an- 

 other leaf and conditions are favorable, such as high 

 temperature and relatively high humidity. Frequent 

 rains and heavy dews are favorable to the spread of this 

 disease. No great harm results from the attack of this 

 fungus, although it may sometimes produce swellings on 

 the stems and petioles and malformations of the leaves. 

 White-rust is much more prevalent in wet weather. It 

 is widely spread, having been found in both the eastern 

 and the central section. 



