Beet Diseases 119 



stroma. The temperature and relative humidity of 

 the air influence the production and infection of 

 conidia. Conidia are generally formed on the lower 

 surface of the leaves, no doubt because these are 

 subject to a higher humidity. 



Control. Infected material should be destroyed 

 by fire. Spraying with Bordeaux mixture 4-4-50 is 

 also recommended. 



Root Rot 



Caused by Rhizoctonia solani Kuhn. 



Symptoms. This disease produces a damping off 

 of the young seedlings, and on older plants a rotting 

 of the crown. Upon pulling out an infected plant, 

 we find that the outer leaves are dead and dry, while 

 the inner ones are somewhat curled. The roots of 

 such plants invariably are rotted at the crown, the 

 rot generally working inwards to a considerable ex- 

 tent. The peculiarity of this disease is that the 

 lower half of the root is generally sound. Frequent- 

 ly, the rotted crowns are also found to be cracked 

 at various places. Beets thus affected are worthless 

 for the market. For a description of the fungus 

 see p. 20. 



Control. There are no methods of control known. 

 The factors which favor the trouble are poor drain- 

 age, an excess of soil moisture, and lack of suffi- 

 cient ventilation. Every step taken to overcome 

 these will in a degree help to control the rot. Soil 

 sterilization is also recommended. 



Root Knot, see Nematode, p. 28 (fig. 16, a.). 



