VEGETABLE AND FIELD CHOPS 201 



but also carry the disease to the field to infect other plants. 

 One infected seed in a thousand is enough to infect the 

 field, and spraying is not effective ^ to check the spread of 

 the disease after infection occurs. Since no effective rem- 

 edy is at hand except the use of healthy seed, the greatest 

 care should be given to this point. Home fall-grown seed 

 known to be free from disease is preferable to seed of un- 

 known origin that is perhaps diseased. If a few seeds 

 known to be free from disease can be secured and multi- 

 plied in a special seed plot, they will give clean seed for 

 future use. Treatment of the seed to kill the fungus is not 

 yet upon a practica))le l^asis. Clean culture, the removal 

 from the field and destruction of diseased stalks and plant 

 parts eliminates a source of spring infection which may be 

 important. 



Rust {Uromyces appendiculahis (Pers.) Link). — This 

 rust may be recognized by its sori upon the leaves 

 and occasionally upon other structures. The sori are at 

 first blisters of pinhead size, covered by the epidermis of 

 the plant. Later this covering ruptures and discloses a 

 mass of spores the color of iron rust, or later in the season 

 chestnut colored, which fall away in quantity, smudging, 

 the leaf and spreading the disease. The upper side of the 

 leaf opposite a sorus usually shows a spot, pallid, yellowish, 

 lacking in true leaf-green color. Sori are sometimes found 

 upon the upper surface, but not so frequently as upon 

 the lower. 



The rust usually develops somewhat late in the season 

 and is not so destructive as are many of the other bean 

 troubles. 



' Whetzel, H. H., N.Y. (Cornell) Agr. Exp. Sta. Bui. 255, May, 1908. 



