EEPOKT OF THE APPLE AND PEAR COXFERENCE. 



47 



CANKEE: ITS CAUSE AND CUEE. 



By Mr. James Douglas, F.E.H.S., Ilford, Essex. 



This troublesome disease in fruit trees lias very frequently 

 been the subject of discussion in the gardening periodicals and 

 elsewhere. Nearly every gardener has had to deal with it in his 

 experience of the details of fruit culture, and as I had consider- 

 able experience of it, some twenty-five years ago, in an old Essex 

 garden, I may at least claim some practical knowledge of the 

 subject. 



At the outset it may be taken for granted that it is absolutely 

 necessary to ascertain the cause of a disease before any attempt 

 can be made to find a remedy. The late Mr. Eobert Thompson, 

 author of the Gardener's Assistant," and Superintendent of 

 the Eoyal Horticultural Society's Garden at Chiswick, writes on 

 canker with considerable diffidence. In the work above cited, page 

 381, he says: " The cause of canker is imperfectly understood, 

 and so consequently is an effectual remedy." 



His idea of the causes of canker, as summarised in his admir- 

 able work, are : — 



1. Sudden checks to the vegetation of the tree, especially in 

 spring and the early part of summer. 



2. Derangements of the flow of sap from vicissitudes of heat 

 and cold, as well as of moisture and dryness. 



3. Unskilful and severe pruning. 



4. Vitiation of the sap by deleterious substances in the soil or 

 subsoil. 



5. Dryness at the root doubtless gives rise to a species of 

 canker, which manifests itself on the younger branches and on 

 the shoots. 



Eeferring also to Lindley's " Theory of Horticulture," page 

 110, it is stated that a Mr. Eeid, of Balcarras, had shown " that 

 one of the causes of canker and immature fruit even in orchards 

 is the coldness of the soil. He found that in a cankered orchard 

 the roots of the trees had entered the earth to the depth of three 

 feet ; and he also ascertained that during the summer months 

 the average heat of the soil at six inches below the surface was 

 01 degrees ; at nine inches, 57 degrees ; at eighteen inches, 50 

 degrees ; and at three feet, 44 degrees. He took measures to 

 confine the roots to the soil near the surface, and the conse- 

 quence was the disappearance of canker and perfect ripening of 

 the fruit. 



Another cause has been suggested, viz.: Insect agency. But 

 this view of the matter will probably not be sustained by prac- 

 tical gardeners generally. That insects of various kinds, includ- 

 ing that troublesome pest American blight {Aphis lanigcra), will 



