PART VIII 



Bulletins and Papers of Interest to Farmers and 



Stock Growers 



CABBAGE DISEASES. 

 By I. E. Melhus and I. H. Vogel. 



Cabbage diseases are the chief limiting factor in profitable commer- 

 cial cabbage growing in Iov»'a. The most destructive of these are black- 

 leg, black-rot, and cabbage yellows. Any one may destroy the greater 

 portion of a crop. The first two are known to be distributed with the 

 seed and cause infection of the young plants in the seed bed. Some of 

 these naturally find their way into the field and under favorable con'- 

 ditions become destructive. Cabbage yellows may also be distributed 

 with the seed but is probably more commonly spread with the plants 

 by the soil adhering to the roots. 



These diseases may 

 remain alive in the soil 

 for from two to twelve 

 years. The first step in 

 successful cabbage 

 growing, therefore, is to 

 prevent the develop- 

 ment of these diseases. 

 In order to do this the 

 seed should be treated 

 and the plants grown 

 in soil free from dis- 

 ease. 



r~ 



*■...* 



BLACK-LEG 



Black-leg is caused 

 by a fungous organism 

 whose presence is indi- 

 cated by sunken spots 

 with a purplish border 

 on the stem just above 

 the surface of the soil. 

 The spots increase in 

 size and depth until the 

 stem is girdled as 

 shown in fig. 1. This 

 may occur either on the 

 seedling or the nearly 

 mature plant. When 

 the infested tissues die, 

 small black dots, known 

 as pycnidia, are formed, 

 on the sunken spots. 



The pores are borne 

 in the pycnidia, which 

 enables' the disease to live over from one year to the next. These 

 may either remain attached to the old cabbage stumps in the fields 

 or be set free in the soil. The spores may also adhere to the seeds. 

 It is plain, therefore, that infection may come about either thru the 

 Infested, refuse in the soil or the seedlings propagated from infected 

 seed. 



Fig-. 1. 

 leg; 



Cabbage plant Infected with black- 

 the disease has girdled the stem. 



