VI 



IRISH GARDENING. 



Apple Canker (Nectria ditissima). 



Ai'Pl/K Caxkior is one of tlie most <lfs( luctivc 

 <lisoa.scs with Avhicli fruit !j:i'owev.s lui vi- to contend. 

 11. is ."t, sci'iovis nicnaci' to fruit trees on the Con- 

 tinent of luirope. -whilst in England it lias ruined 

 many a plantation and placed certifiin kinds of 

 apples verylarfXely outside the pale of connnercial 

 cultivation. Though the term "canker" is 

 oftien applied to various open Avoiuids where the 

 bark is swollen and rugged, tiie true aj)ple 

 canker, as understood in Britain, is a sjjecilic 

 disease, and is caused by the nuniite fungus 

 Xectria ditissima. The same fungus also causes 

 cauker in the pear, though the disease is ufit so 

 frequent in this tree as in the apple. 



The wounds may occur anywhere on tlie 

 })ranches, but are found most frequently at a 

 node or at the junction of a small branch 

 with a larger. 



The commencement of the ca.nker-wo\ind and 

 the various stages which foUoAv nuiy readily he 

 observed if a diseased tree is studied with a iitlle 

 care. Tile young stages will be seen as small 

 de]>ressed areas, which gradually break aw;iA- 

 from the. suTrounding part of the shoot and are 

 somewliat darker in hue. Such areas very fre- 

 quenth'. but not invariably, originate around 

 a dead twig, and are caused by the activity 

 of the fungus which lias gained an entrance 

 to the tissues. This small damaged area 

 increases -in size and usually becomes more oi' 

 less elongated in outline. The tissue in th<' 

 central portion dies and gradually dfcays. so 

 (hat the damaged area assumes the form of 'jmi 

 open wound surrounded in later stages by rugged 

 bark. Such Avounds. termed "canker'" by 

 gardenei's, are found in many plants and may be 

 produced by a variety of causes. In the aj)]ile 

 canker is due to the fungus Xectria ditissima 

 althougli, as exjilaiued below, tlie injur>" caused 

 by \\'ooll\' .Vjihis is often very similar in ajiix-ar- 

 auce. and in fact the two pests are not infre- 

 quently found together and aid each oilier in the 

 d.iiiiage thev cjiuse. One of the Jiiost marked 



j features of aijple canker is the presence of more 

 I or les.s regular concentric rings around, the Avound. 

 and' it may frequently be recognisM by these 

 even i^i the absence of the fruits of the fungus. 



As the disease progresses the Avound enlarge- 

 and a mass of swollen tissue, due to the repeated 

 formation of callus by the branch, arises around 

 it. The sul)se(iuent beha.Aiour varies uiujei 

 different circumstances and Avith different Aari. 

 ties of apple. In, many cases the Avound is con 

 fined to one side of the branch and the branch 

 continues to live for many years. In other cases 

 the parasite rings, that is completely encircles, 

 the branch oi- shoot, and causes its deatli 

 I'rovidecl the branch is not ringed the sap 

 I onlinues to flow, and such branches remain 

 alive and may even gmu' and yield lieaAy crops 

 of small fruit. 



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