39 



APPLE TREE CANKERS. 



W. Lochhead, Macdonald College. 



In recent years considerable attention has been given to those appearances 

 on apple trees commonly designated as Cankers, on account of the fact that but 

 few orchards in the Province can be said to be free from them. Some of the best 

 apple trees in many orchards have succumbed to the attacks of the canker, and 

 the owners are already inquiring anxiously for information regarding the nature 

 of this disease, and the best methods of combating it. 



As a result of the observations and investigations carried on during the last 

 few years it can now be definitely stated that there are several kinds of canker, 

 each possessing its own peculiar canker, and each induced by a different cause. 



Cankers are wounds kept open by the action of some agency in spite of the 

 attempts of the tissues to heal them. As a rule they are conspicuous, whenever 

 they are present, either by the absence of bark, or by the abnormal roughness of 

 the bark clinging closely to the adjacent tissues, or by a large mass of dead and 

 disorganized wood. 



Cankers may be grouped and discussed according to the agencies causing 

 them: — 1. Sun-scald and Sun-burn Canker; 2. Frost Canker; 3. Nectria Canker; 

 4. Bitter-rot Canker; 5. Black-rot Canker; 6. Woolly-Aphis Canker; 7. Blister 

 Canker, and 8. Twig Blight Canker. 



Sun-scald and Frost Canker. — Such a canker is nearly always observed 

 on the south or south-west side of the tree. During warm days in winter the 

 tissues on the sunny side of the trunk are warmed up and are incited to renewed 

 acti\dty. Such tissues always suffer from subsequent freezing by the loss of 

 water from the cells. Afterwards they contract and crack open. Similar effects 

 are produced by the action of very dry, cold winds, which cause the tissues to lose 

 much water. The tissues destroyed in these ways become disorganized; the 

 bark falls away from the wood, and saprophytic fungi effect an entrance before 

 the wounds can be closed up by the rapid growth of the healthy tissue bordering 

 on the wound. 



European or Nectria Canker (Nectria ditissima). — This canker, which is 

 the common one in orchards in Europe, has been identified for a certainty in but 

 few localities in Canada and the United States. It is probable that it is in our 

 Quebec orchards as it has been observed in New York State and Nova Scotia. 



(Fig. 1). 



