322 Diseases of Greenhouse Crops 



spore heads of this organism (fig. 65, a) when ripe 

 are shot off into the air and stick to any object on 

 which they may alight, which in this case happened 

 to be the foliage and blossoms of the roses. The 

 mechanical spotting here referred to was caused by 

 nothing more than the presence of the spore heads 

 of the fungus. The trouble ceased when the fimgus 

 no longer produced spores. The specking on the 

 rose blossoms was not serious enough to injure their 

 market value. 



Rose Rusts 



Caused by Phragmidium species. 



Rose rusts are more commonly found on plants 

 growing in the open. These, however, may be intro- 

 duced indoors with cuttings, or plants first started 

 in the nursery. 



Phragmidium suhcorticum (Schrank) Wint. 

 This fungus causes the true rust of roses. It is very 

 prevalent in Europe, is of little importance in the 

 United States. On the leaves this rust appears in 

 small circular spots (fig. 65, c), and on the stems 

 and petioles in large powdery masses. At first the 

 sori or spore clusters are orange-yellow, but later 

 turn brick red. 



Phragmidium speciosum Fr. This fungus is the 

 cause of a rose rust which affects the stems and 

 which rarely appears on any other part of the plant. 

 The sori are black and irregularly scattered. The 

 causal fungus is carried over from year to year as 

 viable mycelium in the affected host. Cutting out 



