190 Ap2>le Canker Fungus — Leaf Scar Infection 



seedlings do not always develop into cankers, owing to the formation of 

 a phellogen which excludes infected material in exactly the same way 

 as has been found to exist when shallow cuts are inoculated artificially. 

 Such excluded material can be recognised hanging on to the edge of the 

 infected leaf scar (Plate III, Fig, 2). 



CONTROL CONSIDERATIONS. 



The economic loss by the leaf scar infection is considerably reduced 

 in the case of bush trees by the practice of winter pruning. In this 

 process, most of the infected wood is cut out, although some is occasion- 

 ally overlooked, and also infection may take place after the pruning has 

 been done. In the case of young trees the loss is especially important, 

 as a large quantity of new growth is required to build up the main stems. 

 A few bud infections on a young tree usually means a considerable loss 

 to the tree. At Long Ashton not a few cases of grafts of varieties so 

 resistant as that of Bramley's Seedling, have been totally destroyed by 

 infection of the leaf scar. With orchard trees, where little pruning is 

 done, this type of infection is most serious, and it is probable that in 

 those cases where the trees suddenly canker all over, it is leaf scar 

 infection which is responsible for the damage. The sudden increase in the 

 number of infections on the Kingston Black x Medaille d'Or seedlings, 

 as recorded above, shows that such a state of things does occur. 



There does not appear to be any valid reason why spraying of the 

 leaf scars, especially before the buds burst, should not prove a successful 

 control measure in the case of spring infections of the canker fungus. 

 Preliminary trials (4) with this end in view were started in December 

 1919. Twenty branches were selected from the Kingston Black x Me- 

 daille d'Or seedlings and ten of these branches were sprayed with copper 

 stearate on December 16, 1919, the remaining ten being left as controls. 

 Counts made on May 23, 1920, showed that the number of new cankers on 

 the sprayed branches was reduced from 299 in 1919 to 62 in 1920, whilst 

 the number on the controls increased from 135 in 1919 to 299 in 1920. 

 Additional infections took place subsequently, but in December 1920 

 re-counts showed a marked reduction on the sprayed branches, the 

 numbers then being 179 for the sprayed and 500 for the controls. These 

 results are sufficiently promising to warrant the further trials which are 

 now being carried out. 



'^ Reference must be made here to the spraying experiments carried 

 out by Grubb(5) at East Mailing during the last two years. By spraying 

 with lime-sulphur or Bordeaux, in May and again in June, he was able 



