Radish Diseases 175 



the rootlets have been rotted off and that the main 

 root, too, has rotted at various intervals* (fig. 35). 



Control. This disease may be controlled in the 

 same way as damping off (see pp. 32-43). 



Downy Mildew, see Cauliflower, p. 127. 



Damping Off, see Rhizoctonia, p. 20. 



Root Knot, see Nematode, p. 28. 



Rhubarb 



Cultural Considerations. Rhubarb is a popular 

 greenhouse crop, and is extensively forced for win- 

 ter use. Greenhouse rhubarb is superior in quality 

 and in texture to the out-of-doors variety. The 

 plant may grow in total darkness, but a diffused 

 dim light is advisable. The roots before being 

 planted should be thoroughly frozen for a few days, 

 then given a short rest. In the milder climates of 

 the South, the roots should be dried before planting. 

 Both of these treatments will accelerate growth. 

 When well established the plants need not be 

 watered more than twice a week. The temperature 

 for rapid growth ranges from 50 to ^$ or 60 degrees 

 F. Under lower temperatures, the plants will re- 

 quire a longer time to mature. The varieties which 

 lend themselves well to forcing are the Paragon, 

 Mammoth, Linnseus, Strawberry, and Victoria. 



*A description of the causal organism is given in the author's 

 previous volume, "Diseases of Truck Crops and their Control," 

 p. 2IO, 1918. (E. P. Dutton & Co., Nevf York.) 



