S. p. Wiltshire 191 



to record a considerable reduction of canker infections. The best times 

 for spraying are obviously immediately after defoliation or before the 

 breaking of the buds and it is somewhat difficult to see why spraying 

 in May and June should be markedly effective. Until defoliation in the 

 autumn no infection would occur on the 1920 wood and it is doubtful if 

 spraying in May or June would affect this appreciably. As regards the 

 1919 wood, however, the main autumn and spring infections would also 

 have occurred before the sprayings and would not be affected by them. 

 But as already mentioned the leaf scar infection of the previous season's 

 wood continues slowly throughout the summer and possibly against this 

 infection the spraying was effective. 



The existence of autumn infection of leaf scars naturally increases 

 very considerably the difficulty of the control of the disease by spraying 

 in the case of varieties so affected. First of all the spraying of the leaf 

 scars immediately after defohation is dangerous, because at that time 

 the fruit still remains hanging on the tree in many instances and spray 

 fluids may spot the fruit. Further, the spraying of ripe fruit with a 

 copper fungicide is open to obvious objection, and as regards sulphur 

 sprays as an alternative, the fact that the canker fungus does not appear 

 to be very sensitive to sulphur rather discounts their effectiveness{6). 

 Another difficulty in autumn spraying for canker is the rapidity of 

 infection, which results in many leaf scars being infected before defolia- 

 tion is complete. At least two sprayings at the time of defoliation there- 

 fore would appear to be necessary to control the disease even if suitable 

 spray fluids can be found. 



Although spraying treatment for autumn infection therefore is not 

 altogether promising, other treatments for reducing the amount of in- 

 fection may yet be possible. Vigorous trees usually hold their leaves 

 longer than weakly ones and any treatment therefore which would tend 

 to increase the vigour of the trees, may by delaying autumn defoliation 

 reduce the risk of infection. 



SIBIMARY. 



The infection of the apple stem by the canker fungus through the 

 leaf scars is described. 



The fungus appears to enter through small cracks which appear in 

 the leaf scar tissues, in the autumn immediately after defohation and 

 in the spring when the buds are sweUing. 



The possibihty of preventing this infection by disinfecting the leaf 

 scars by fungicides is discussed and results of preUminary trials recorded. 



