154 Diseases of Economic Plants 



In fields where the disease is well established upon stems 

 and leaves the damage is great in loss of starch-producing 

 power. Still greater loss follows from the spread of the 

 disease to the pods, the unsightliness of the spotted pods 

 greatly injuring their salability. 



Since the spores are spread only when they are wet, 

 handling or disturbing the vines in any way while the dew 

 or rain is still upon them should be avoided. Seeds already 

 bearing the fungus, i. e., spotted seeds, should never be 

 planted, since they not only raise sick plants, but also carry 

 the disease to the field to infect other plants. One infected 

 seed may carry contagion to the field. Spraying is not effec- 

 tive. Since no remedy 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 unknown origin. If a few seeds known to be free 

 from disease can be secured and multiplied in a special seed 

 plot, they will give clean seed for future use. 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 appendiailahis (Pers.) Link). — • 

 This rust may be recognized by its sori upon the leaves and 

 occasionally upon other structures. The sori appear at 

 first as 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 foimd 

 upon the upper surface, but not so frequently as upon the 

 lower. 



Rust usually develops somewhat late in the season and 

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

 troubles, though in certain localities, e. g., in Virginia, the 

 crop is sometimes completely destroyed. 



