REPOBT OF THE SOCIETY 67 



PEONY DISEASES 

 by J. G. Coulson 



The peony is one of the important economic ornamental plants and some 

 growers have a good deal of capital invested in them. Very little has been 

 written concerning the diseases of the peonj' and it is for the most part consi- 

 dered to be a sturdy perennial plant remarkably free from all such troubles, 

 but a little observation any season will show that the different varieties are 

 more or less subject to quite a number of diseases. The amount of infection 

 undoubtedly will be found to var\' a good deal, depending upon the season 

 and other conditions, but during the last two summers that the diseases of 

 this plant have been under observation at Macdonald College most varieties 

 have shown severe infections. Last summer we. received several inquiries 

 concerning diseased conditions of peony plants and this with our own obser- 

 vations would lead us to believe that disease is quite general in Quebec and 

 Ontario. 



Saccardo lists 42 fungi found upon the peony. These may be grouped 

 as follows: 



On living leaves 18. 



On living stems 5. 



On leaving leaves and stems 2. 



On fruits 1 . 



On underground parts 1 . 



On dying leaves 3. 



On dead parts 12. 



This gives a total of thirty fungi found upon living parts of the plant 

 and we may conclude that at least the large majority are disease producing. 

 There is no reason to believe that this list should include all the fungi which 

 cause disease in the peony. Our work which was begun a year ago this fall 

 (1921) at the suggestion of Dr. Dickson has shown the peony to be subject to 

 at least seven different distinct diseases. These will now in turn be briefly 

 described. The first two diseases have been known for a long time and will 

 merely be mentioned. 



1. Botrytis blight — {Botrytis Pceonice Oud). 



This is generally considered to be the most trouble some and most common 

 disease of the peony and is well known to everyone as producing "blasted" 

 or brown and unexpanded buds, or large dead spots lipon leaves and stems. 



2. Cladosporium leaf blotch — (Cladosporium Pceonioe Pass.) 



This produces large blotches, purple above and chestnut-brown below, 

 upon the leaves. Estimated infection for all varieties 5%. 



