320 Diseases of Greenhouse Crops 



Blossom Blight 

 Cause, unknown. 



Symptoms, The trouble manifests itself in the 

 failure of the buds to open. At first the buds 

 seem to develop normally. Soon, however, the 

 outer petals wrinkle, turn yellow or straw colored, 

 and stop growing. Occasionally the buds open par- 

 tially, but fail to attain normal size. The true cause 

 of the disease is unknown, although, as believed by 

 Stevens and Hall,* it may be due to some physio- 

 logical disorder in the metabolism of the plant. 

 No control method is known. 



Crown Gall 



Caused by Pseudomonas tumefaciens Sm. and 

 Towns. 



This disease is a very dangerous enemy to out- 

 door roses. It has, however, proved of little eco- 

 nomic importance to indoor roses (fig. 65, b.). 

 For a description of the symptoms and of the or- 

 ganism, see p. 1 15. 



Downy Mildew 



Caused by Feronospora spars a Berk. 

 Symptoms. Downy mildew is more difficult to 

 detect than the powdery mildew. It is also more 



* Stevens, F. L., and Hall, J. G., North Carolina Agr. Expt. 

 Sta., Thirty-first Ann. Rept.: 78-79, 1908. 



