200 "Spotting" of Apples in Great Britain 



but that the varieties preferred by the one are not necessarily those 

 preferred by the other. But the varieties Rival, Wealthy and Allington 

 Pippin, in season from October to December inclusive, were inoculated 

 when unripe whereas Cardinal, Grenadier and Potts's Seedling, in season 

 from August to October inclusive, were inoculated when ripe. Hence 

 the inoculations in the two cases are not strictly comparable since the 

 varieties were not inoculated at the same phase of apple development. 

 The supposition that Pleospora pomorum and Polyopeus purpureus each 

 exhibit a preference for varieties, for example Rival and Cardinal 

 respectively, is therefore open to the objection that a given variety may 

 be susceptible to one fungus at an early stage of its development and to 

 another at a later stage; in fact, there may be a definite fungal succession. 

 Questions of this kind can only be settled conclusively by carrying out, 

 throughout the season, continuous comparative series of inoculations on 

 specially selected varieties. Certain subsidiary phenomena for example, 

 "arrested spotting" and recrudescence of "spotting" after a period of 

 rest, would then be better understood. Considerable help would be 

 afforded by a parallel study of the seasonal chemical changes taking place 

 in the varieties selected for experimental purposes. 



Outdoor measures. 



The risks of summer infection could be considerably reduced by 

 spraying with Burgundy mixture when the fruit is young. Very probably 

 a weak solution thoroughly applied, similar to that successfully used 

 at Wisley by the authors 1 to prevent the infection of gooseberries by 

 the American gooseberry mildew, would serve the purpose. The treat- 

 ment should be repeated each year, for until the life-histories of the 

 fungi concerned in "spotting" and the various sources of summer 

 infection are completely known, it is impossible to take comprehensive 

 measures against seasonal recurrence. The success of spraying as a means 

 of control has been repeatedly demonstrated in America by Lamson 2 

 and others. 



Indoor measures. 



Summer spraying should practically prevent the appearance of 

 "spotting" in store unless the fungi exist in the fruit-room itself. Where 

 no spraying has been practised, the development of "spotting" could 



1 Home, Arthur S., in The Gardeners' Chronicle, lix, p. 310 (June 10. 1916); and 

 Home, Eleanor V., in The Garden, lxxxi, No. 2374, 174 (May 19, 1917). 



2 Lamson, W. H. N. H. Coll. Bulls. Nos. 27 (Apr. 1895), 45 (May, 1897), 65 (May, 1899), 

 101 (Apr. 1903). 



