354 Diseases of Greenhouse Crops 



patches, the presence of which greatly distorts the 

 attacked parts. All the three stages of the causal 

 organism, secia, uredinia, and the telia are present 

 on the same fungus. 



The Organism. The seciospores are orange yellow, 

 subglobose, and finely warty. The uredospores are 

 roundish and brown, possessing tiny warts. The 

 teleutospores are black, elliptic to oblong, with 

 thickened tip, and with a very slight constriction. 



Control. Violet rust is most prevalent on out- 

 of-door plants, especially on the wild varieties. The 

 disease is not of economic importance on indoor vio- 

 lets. 



Crown Rot 



Caused by Sclerotinia libertiana Fcl. 



This disease causes a rot of the crown as well as 

 of the runners. This trouble is common in the cut- 

 ting bed in which case it produces a damping off. 

 In either case, the affected parts become soft and 

 slimy. The disease is found only in leaky houses, 

 or in beds with leaky water pipes. Attention to 

 these points will check the trouble. For further 

 description of the causal organism, see lettuce, p, 151. 



Thielavia Root Rot 



Caused by Thielavia basicola (B. and Br.) Zopf. 



Thielavia root rot is perhaps one of the most im- 

 portant troubles of greenhouse violet. The disease 

 also attacks sweet peas, cyclamens, and asters. 



