198 A Blossom Wilt and Canker of Apple Trees 



conidia on the ripening fruit mucli less readily than M. fructigena, and 

 this probably accounts for its inability to establish itself on the mature 

 apples, for the chief sources of infection from this fungus (i.e. the 

 pustules on the cankers and spurs killed in the previous season) have 

 shed most of their conidia and are becoming desiccated at the time when 

 the apples are reaching maturity. As indicated earlier in this paper 

 the newly formed cankers do not produce conidia until long after the 

 fruit is picked. 



The blackening of the skin of apples produced by the blossom wilt 

 fungus may also be caused by M. fructujena and by the hyaline grey 

 Monilia, particularly on the mature fruit, but the result takes place 

 much more gradually. Black apples with few or no pustules are 

 frequently found among stored fruit; this condition appears to be 

 brought about by M. fructigena which has invariably been isolated by 

 the writer from such apples obtained from fruit growers in Kent. 



Spinks(22) finds that a similar "Black Rot"' of cider apples is also to 

 be attributed to M. fructigena. 



VI. Control Measures. 



It is evident that cutting away the dead spurs and cankers removes 

 the chief source of infection, and an experiment, carried out on the row 

 of trees of the Warner's King variety referred to in preceding pages, 

 has demonstrated that where this can be done thoroughly the results 

 are highly satisfactory. 



Ten trees at one end of the row were carefully pruned by the writer 

 on June 15 and 17, 1915, and so far as could be seen at the time every 

 withered truss was cut away until all the dead discoloured (brown) 

 tissues of the spur were removed. In those cases where cankers had 

 developed on the branches the operation involved the removal of dead 

 bark and wood in those places, until a clean cut, showing healthy tissues 

 only was made. The trees were not treated in any other way and the 

 wounds made by the pruning knife were left exposed. In all over 220 

 dead spurs were removed from these trees. When these ten trees were 

 examined in the summer of 1916 it was found that five were quite free 

 from the disease, one tree had but one dead truss, three had two each, 

 and one had six dead trusses ; a search on the last mentioned tree how- 

 ever revealed the fact that two dead spurs had been overlooked during 

 the pruning operations and these now bore a number of Monilia 

 pustules. 



The rest of the trees (fourteen in nund)er) in the same row had been 



