66 



Canker ox Apple and Pear Trees. 



It^has been considered that only trees that are weakly and 

 unhealthy are liable to the attack of the Scolytus rugulosus ; 

 but this is by no means the case, as trees, apparently quite 

 healthy and vigorous, have been found to be infested by this 

 beetle, which seemed to be the sole cause of the mischief 

 occasioned in these cases. Similar observations have been 

 made in the United States of America, where perfectly 

 vigorous trees have been attacked by the beetle. It would 

 seem, therefore, that healthy and unhealthy trees are alike 

 liable to this infestation. 



The first indication of the attack is the shrivelling of the 

 tips of the smaller branches, in which small holes and tun- 

 nels will be found, and, on inspection, it will be seen that the 

 tunnels and borings extend throughout them to the larger 

 branches, and even to the trunk. A badly infested tree 

 should be cut down and burned during the winter, in order to 

 prevent the beetles from flying to other trees in the spring. In 

 cases of recent infestation it is of great benefit to work 

 paraffin oil into the infested parts with a brush, so that it 

 may enter the holes made by the beetles. 



Canker on Apple and Pear Trees. 



There is more than one disorder of apple trees wrongfully 

 designated as " canker," and injuries from hail, frost, and 

 other climatic causes are often generalised under this term. 

 But what experts mean by canker is the disease occasioned 

 by the fungus Nectria ditissima. It is known in France as 

 Chancre^ and in Germany as Krebs> and it is unmistakable, 

 as in one of the stages of the affection little coral-red dots, 

 which are the perithecia or spore cases of the parasite, are 

 found in the folds of the infected bark. 



The action of true canker is, as common observation indi- 

 cates, comparatively slow. Hartig states, in his Baumkrank- 

 heiterii that it does not usually extend more than half an 

 inch in a year ; while in other attacks attributed to " canker' - 



