[ 



Primrose Diseases 317 



often destroyed before the other half shows any- 

 marked deterioration. 



Little is known of the causal organism. The de- 

 struction by fire of diseased material and spraying 

 with a standard fungicide is recommended. 



Leaf Spot 



Caused by Ascochyta primulcz Wail. 



Symptoms. The presence of the disease is shown 

 by oval spots, which spread and often involve the 

 entire leaf. This disease may often be mistaken 

 for the spotting caused by Phyllosticta primulicola. 

 However, a microscopical examination will distin- 

 guish the two organisms. 



Leaf Blotch 



Caused by Ramularia primul^z Thun. 



Symptoms. The presence of the disease is shown 

 by large yellow blotches in the ashen colored cen- 

 ters of which are borne the spores (fig. 63, d.). 



The Organism. The conidiophores grow on both 

 sides of the spots, and are rarely branched, con- 

 tinuous and somewhat denticulate. The conidia are 

 thick but taper towards both ends. Their structure 

 is continuous or one septate. 



Control. This disease may be kept in check by 

 spraying the plants with a standard fungicide. In- 

 fected material should be destroyed by fire. 



