124 Diseases of Greenhouse Crops 



by a dark border. The diseased leaves become yel- 

 low and drop off prematurely. The trouble appar- 

 ently does not attack the cauliflower head. The same 

 disease may also attack the radish. 



The Organism. The disease is produced by Fseu- 

 domonas maculicolum^ a rod-shaped organism, with 

 rounded ends, usually forming long chains in cer- 

 tain media, but producing no spores. The organism 

 is actively motile by means of polar flagella. Invo- 

 lution forms are produced in alkaline beef bouillon; 

 and pseudo-zoogloeae occur in acid beef bouillon. 

 No gas is produced and the organism is aerobic. It 

 is killed by drying and exposure to light. 



Control. Badly diseased plants should be pulled 

 up and destroyed. Spraying with 4-4-50 Bordeaux 

 is recommended. In spraying cauliflower with cop- 

 per compounds, and especially if the latter are in a 

 concentration somewhat stronger than the plant can 

 stand, numerous warts will appear on the leaves in 

 about three days after spraying. These warts should 

 not be mistaken for a disease induced by a parasitic 

 organism. The wart formation is apparently due 

 to a stimulation from the salts absorbed by the host 

 cells. 



Black Rot 



Caused by Pseudomonas campestris (Pammel) 

 Ew. Sm. 



The disease is known both as stem rot and black 

 rot. The latter perhaps is the more common name. 

 Symptoms. Black rot has distinct symptoms 



