DISEASES IN GREENHOUSE 119 



grows on the surface of the leaves, thus 

 giving them the white powdery appearance 

 (fig. 15). Affected leaves eventually lose 

 their green color, shrivel and fall off pre- 

 maturely. The perfect stage of this fun- 

 gus is found on fallen and dead leaves. 

 Powdery mildew is perhaps universally 

 found in every greenhouse where sweet 

 peas are grown. It is worse in over- 

 watered houses, and in overheated houses 

 with excess of moisture. Powdery mil- 

 dew is perhaps the easiest disease to con- 

 trol. 



STEM OR COLLAR ROT 



Sclerotinia libertiana Fckl. 



Observations seem to indicate that this 

 disease is limited to sweet peas grown un- 

 der glass. A special effort was made to 

 find this disease outdoors, but without suc- 

 cess. Under certain conditions unfavor- 



