172 Diseases of Greenhouse Crops 



stem of the plant loses its green color, dries up, and 

 dies. On pulling out a plant freshly wilted, we 

 find a shrunken discolored area at the foot of the 

 stem, slightly below ground level. In more ad- 

 vanced stages, the shrunken area is covered by a 

 delicate web of white mycelial threads, and after the 

 death of the plant numerous brown mustardlike 

 sclerotia are found on the surface of the affected 

 tissue. 



Control. The causal fungus is introduced in the 

 greenhouse with infected soil or manure. Soil ster- 

 ilization with steam or formaldehyde (see pp. 32- 

 43) is recommended. 



