ONION SMUT 223 



ONION SMUT 



{Urocystis cepulae, Frost.) 



This disease is up to the present only known to attack 

 the cultivated onion, and develops during the seedling stage 

 of the host. As a rule, the first leaf shows the disease before 

 the second leaf is developed, generally appearing on succes- 

 sive leaves in the order of their development ; the outer tunic 

 of the bulb eventually becomes infected. When the fungus 

 is mature, the epidermis is ruptured and the spores appear on 

 the surface under the form of large, black, powdery streaks. 



Sometimes the first leaf alone is attacked, when the 

 plant continues to grow ; if more leaves are attacked, the 

 seedling soon perishes. 



White varieties of onion appear to be most susceptible 

 to the disease. 



Preventive Means, — The spores are shed on the 

 ground in immense numbers, and great care should be 

 taken not to transport such infected soil to new and 

 uninfected localities by means of tools, shoes, etc. It is 

 highly probable that the seedlings are infected by smut 

 spores present in the soil at the earliest stage of growth, 

 and cannot be infected at a later stage ; hence it is 

 recommended that onions should be transplanted, for even 

 if planted in ground containing smut, the plants remain 

 free from the disease owing to the period of possible 

 inoculation having been passed. Furthermore, apart from 

 the disease, it is maintained that transplanted onions yield 

 a better crop and mature earlier than onions that have not 

 been transplanted. All diseased plants should be collected 

 when the onions are being weeded and thinned. Where 

 soil has become infected with smut-spores, onions should 



