Commercial Gardening 



is killed for some distance round such diseased patches. These cankered 

 patches, if allowed to remain, produce spores each season in succession, 

 which infect the young fruit. The cankers form on the previous year's 

 fruit spurs, also on branches up to 3 in. in diameter. 



Smaller branches and spurs showing the disease should be removed, 

 and cankers should be cut out of the larger branches, and the wounds at 

 once coated with gas tar. When the fruit is attacked when quite young, 

 it usually remains on the branches in a mummified condition until the 

 following season, when fungus spores are produced that infect the young 

 fruit. All such hanging diseased fruit should be removed, as should also 

 all diseased fallen fruit. Pigs are quite capable of accomplishing this 

 object, if for other reasons they can be allowed to enter the orchard. 



Where the disease has existed, the trees should be sprayed with Bor- 

 deaux mixture, half strength, the first application, commencing just when 

 the fruit is set. 



Apple-tree Canker (Nectria ditissima). This disease is much more 

 prevalent now than in past times; reasons for this will be given later. 



As a rule it is popularly be- 

 lieved that canker is the result 

 of a tree growing under un- 

 favourable conditions. This is 

 not correct, the disease is directly 

 due to the action of a fungus, 

 but at the same time the fungus 

 may be greatly assisted in its 

 work of destruction by the tree 

 being weakly, due to bad culti- 

 vation or other causes. The 

 symptoms of the presence of 

 canker, as the name denotes, are 

 a rugged or cankered appear- 

 ance of the bark, which often 

 commences in the fork of a 

 branch. When first attacked, 

 the bark usually shows several 

 cracks arranged in a concentric 

 manner, and as the bark is killed 

 by the fungus it becomes dry 

 and falls away, exposing the 

 wood, which is also eaten away. 

 A callus forms at the edge of 



the wound, which in turn is attacked by the fungus and killed here and 

 there, producing a rugged mass round the edge of the wound, which 

 continues to increase in size year by year. If the bark or callus near the 

 edge of a canker wound is carefully examined with a magnifying glass, 

 clusters of minute red bodies (fig. 349) smaller than the head of a small 



Fig. 349. Apple-tree Canker (Nectria ditissima) 



Branches of an apple tree showing the bark destroyed by the 

 fungus. The little white points in the cracks on the diseased 

 parts are the fruits of the fungus, which are of a bright red 

 colour (natural size). (Gard. Chron.) 



