Lettuce Diseases 153 



Cercospora Leaf Spot 



Caused by Cercospora lactuc(Z Stev. 



This disease is as yet of no importance in the 

 United States. The causal fungus attacks the older 

 and lower leaves forming numerous irregular spots. 



Rosette 



Caused by Rhizoctonia solani Kuhn. 



Symptoms. The disease attacks young seedlings 

 by causing a damping off. Transplanted seedlings 

 show infection at an early stage. Unlike healthy 

 plants, they fail to send out new leaflets. The gen- 

 eral growth takes the form of a rosette. The axis 

 bearing leaf remains stunted. The roots show nu- 

 merous deep lesions, and in an advanced stage are 

 considerably rotted (fig. 28, b.). For a description 

 of the causal organism, see p. 20, and for meth- 

 ods of control see Lettuce Drop, p. 151. 



Root Knot, see Nematode, p. 28. 



Mint {Mentha sp,) 



Cultural Considerations. Mint is often forced on 

 a small scale. The plants are easily grown, and re- 

 quire about the same indoor conditions as the let- 

 tuce. 



Diseases of the Mint 



Indoor mint may be subject to but one disease of 

 importance. 



