190 Diseases of Truck Crops 



should be taken to exclude club roots from the seed 

 bed, since many an outbreak of this trouble may be 

 traced back to the use of previously infected seedlings. 



Black Rot 



Caused by Pseudomonas campestris (Pammel) 

 Ew. Sm. 



The disease is known to growers as stem rot and 

 black rot. The latter perhaps is the more common 

 name. The trouble may now be found wherever 

 cabbage is grown on a large scale. 



Symptoms. Black rot has distinct symptoms 

 which cannot easily be confused with other cabbage 

 diseases. On the leaves, the symptoms are mani- 

 fested as a burning appearance on the edges (fig. 

 30 d) and a yellowing of all the affected parts except 

 the veins, which remain blackened. From the mar- 

 gin of the leaves the disease works downwards to the 

 stalk. From there the disease travels up again to 

 the leaves and from there to the stems. The parasite 

 works in the fibro-vascular bundles of the leaves and 

 main stalk, causing a premature defoliation. Occa- 

 sionally, the disease enters one side of the stalk, the 

 latter becoming dwarfed and the cabbage head be- 

 coming one sided. In severe cases of attack, there is 

 a total lack of head formation. In splitting open a 

 stump of an affected plant, we will find a black ring 

 which would correspond to the places of the fibro- 

 vascular bundles invaded by the organism. Smith 1 



1 Smith, E. F., U. S. Dept. of Agr. Farmers Bui., 68: 5-21, 1898. 



