REPORT OF THE SOCIETY 85 



THE BLACK KNOT OF PLUM AND CHERRY 

 C. B. Hutchings, Macdona!d College 



{Plowrightia morbosa, Schwtz) 



The purpose of this paper is to discuss briefly the Black Knot disease 

 of Plum and Cherry from various standpoints, viz: — its history, distribution, 

 appearance, effect on host and its control. 



Black Knot is a very serious and widely distributed disease of the 

 different species of Prunus. It is characterised by the dark, unsightly, 

 wart-like excrescences which appear on the twigs and branches of the 

 host, giving them the appearance of being burnt or charred. It is very 

 noticeable in small gardens, neglected farms and wayside places. Where 

 allowed to remain unchecked the disease will rapidly spread throughout 

 the orchard, and in a few years ruin it. If, however, the trouble is taken in 

 hand when it first appears, it can be easily checked and in time eradicated. 



There are records which show that this orchard pest was noticed as 

 far back as the beginning of the 19th century, but the trouble was not care- 

 fully studied until about 1870. Since then little has been done. 



Black Knot is found very abundantly throughout Great Britain, the 

 United States and Canada, wherever plums and cherries,' wild or culti- 

 vared, are found growing. 



It is particularly bad in the Maritime Provinces, Quebec and New 

 York State, and in parts of Ontario. In the Niagara peninsula where the 

 majority of the cherry and plum orchards of the Dominion are situated, 

 control measures are so carefully carried out that the disease is almost 

 unknown. 



Excepting the wild pear (Amelanchier) upon which it has been reported, 

 the fungus is confined to the various species of Prunus, and may be found 

 on nearly ail varieties of both the wild and cultivated. It appears , how- 

 ever, more disposed toward cherries of the Murillo type, and plums of the 

 Damson variety. It has also been noticed that the disease will attack, in 

 certain seasons only, certain species of plums and cherries and neglect others. 

 This is due possibly to the fungus having- several physiological or biologi- 

 cal forms which restrict themselves to their respective hosts. This matter, 

 however, has not been definitely settled. 



The disease attacks only the woody parts of the host. Usually the 

 Knot does not entirely girdle the branch but appears on one side, extending 



