DISEASES OF CROPS 



955 



Root Rot (Rhizoctonia betce, Kuhn). — This disease causes the outer 

 leaves to turn black and fall. As the disease advances the roots crack and 

 then rot from the crown downward. 



Treatment. — Use lime and rotate crops. 



Scab. — See Potato. 



CABBAGE, CAULIFLOWER, TURNIP, ETC. 



Black Rot (Pseudomonas campestris, Pammel). — This is a bacterial 

 disease which attacks 

 all of the above and 

 many related plants. 

 It starts at the edges 

 of the leaves, causing 

 a blackening of the 

 veins, gradually work- 

 ing downward to the 

 main stalk and then 

 upward and outward 

 until the entire plant is 

 affected. The affected 

 leaves become yellow, 

 wilt and then dry. In 

 advanced stages the 

 disease is accompanied 

 by other rot organisms 

 which cause a pro- 

 nounced odor. 



Treatment. — When 

 once in the soil it is 

 extremely difficult to 

 eradicate. Prevent in- 

 fection by using clean 

 seed, which as a pre- 

 cautionary measure 

 should be soaked for 

 fifteen minutes in for- 

 maldehyde (1 part for- 

 malin to 30 parts 

 water) . 



Club Root or Fin- 

 ger and Toe Disease 



(Plasmodiophora brassicce, Wor.). — This very destructive and well-known 

 disease attacks cabbage and related plants, causing unsightly knotted 

 roots. The diseased plants are dwarfed and fail to develop heads. 



1 From Farmers' Bulletin 488, U.S. Dept. of Agriculture. 



Enlarged Roots op Cabbage Caused by Nematodes. 1 



