138 Diseases of Truck Crops 



Downy Mildew 



Caused by Plasmopara Halstedii (Farl.) B. and D. 



This mildew attacks the Jerusalem artichoke as 

 well as the sunflower. The disease is of little eco- 

 nomic importance. The trouble is apparent as 

 downy whitish patches on the under side of the leaves 

 which soon spread, involving the entire area of the 

 affected foliage. This soon turns yellowish, becomes 

 dry and brittle, and dies. 



Rust 

 Caused by Puccinia helianthi Schw. 



This rust is supposed to be the same as the rust of 

 the sunflower. However, the work of Arthur' shows 

 that no infection takes place when the teliospores 

 from the sunflower are sown on the Jerusalem arti- 

 choke. It is probable that we deal with physiological 

 races. The rust on the artichoke is characterized 

 by numerous spore pimples, yeUow at first but later 

 tviming to dark brown. 



Leaf Blotch 

 Caused by Ramularia cynarce Sacc. 



This disease has as yet proved to be of little 

 economic importance in the United States. In 

 Europe, however, leaf blotch seems to cause con- 



■ Arthur, J. C, Mycologia, 11 :53, igoe 



