APPLE CANKER. 



(Nectria galligena.) 



Apple canker is one of the most destructive diseases with 

 which fruit growers have to contend. It is a serious menace 

 to fruit trees on the continent of Europe, whilst in England 

 it has ruined many a plantation and placed certain kinds of 

 apples very largely outside the pale of commercial cultiva- 

 tion. Though the term " canker " is often applied to various 

 open wounds where the bark is swollen and rugged, the true 

 apple canker, as understood in Britain, is a specific disease, 

 and is caused by the minute fungus Nectria galligena.* The 

 same fungus also causes canker in the pear. 



Description. The general appearance of apple canker will 

 be recognised from the figures accompanying this leaflet. 

 Fig. 1 represents an early stage of the disease, Fig. 2 one 

 which is far advanced. The wounds may occur anywhere 

 on the branches, but are found most frequently at a node or 

 at the junction of a small branch with a larger one. 



The commencement of the canker-wound and the various 

 stages which follow may readily be observed if a diseased 

 tree is studied with a little care. The young stages will be 

 seen as small depressed areas, which gradually break away 

 from the surrounding part of the shoot and are somewhat 

 darker in hue. Such areas very frequently originate at a leaf 

 or scar around a dead twig (Fig. 1), and are caused by the 

 activity of the fungus which has gained an entrance to the 

 tissues. This small damaged area increases in size and 

 usually becomes more or less elongated in outline. The 

 tissue in the central portion dies and gradually decays, so 

 that the damaged area assumes the form of an open wound 

 surrounded in later stages by rugged bark. Such wounds, 

 termed " canker " by gardeners, are found in many plants 

 and may be produced by a variety of causes. In the apple, 

 canker is due to the fungus Nectria galligena, although, as 

 explained below, the injury caused by Woolly Aphis is often 

 very similar in appearance, and in fact the two pests are not 

 infrequently found together and aid each other in the damage 

 they cause. One of the most marked features of apple canker 

 is the presence of more or less regular concentric rings around 

 the wound, and it may frequently be recognised by these even 

 in the absence of the fruits of the fungus. 



As the disease progresses the wound enlarges and a mass 

 of swollen tissue, due to the repeated formation of callus by 

 the branch, arises around it. The subsequent behaviour 

 varies under different circumstances and with different 



* Kecent investigations show that Nectria galligena and not 

 N. ditissima as formerly supposed, is the correct name for this fungns. 



