Vegetable and Field Crops 205 



no increase in the size of the bulb occurs after a severe 

 attack. 



To prevent the spread of the disease, and to lessen the 

 danger from subsequent attacks, a spray of Bordeaux mix- 

 ture, 5-5-50, should be applied as soon as the disease is 

 noticed. Careful supervision and spraying to check re- 

 newed attacks of the fungus, particularly if the weather 

 continues to favor its development, should not be neglected. 

 New growth should also be protected by the use of Bor- 

 deaux mixture. 



Infection in previous years warrants spraying before 

 the disease appears; also throughout the season, reaching all 

 sides of the leaf with the fine spray and using high pressure 

 to make the mixture adhere to the smooth onion leaves. 

 Wet lands are more subject to this disease and should be 

 avoided if possible. It is recommended to rake and burn 

 the dead tops, to destroy the infective spores within them, 

 and to practice crop rotation. 



Black-spot ^^^ (Cleistothecopsis circinans, S. & T., Volu- 

 tella, also known as Vermicularia and Colletotrichum) . — 

 The outer scales of the bulb after harvest often show 

 black growths of peculiar and striking character. They con- 

 sist of central, black dots or very small rings, around which 

 from one to several larger rings are arranged concentrically. 

 Under moist conditions these markings enlarge rapidly by 

 the production of more rings or wavy lines, or, under some 

 circumstances, the whole area may be overgrown with black. 

 Later the disease may extend through the outer bulb scale 

 and into the next and succeeding layers to considerable 

 depth, causing rot. 



While the disease is not conspicuous before harvest, it is 

 really present in the incipient stage upon the bulbs in the 

 field and continues to develop rapidly under storage con- 

 ditions. Here it may pass to new bulbs by contact or by 

 air currents. These dangers are much augmented by a 

 moist atmosphere. While the growth is not retarded ap- 

 preciably by this disease, the value of the onion is often 



