25 



in the form of small, rounded, grey pustules similar to those 

 found on the spurs. 



The Attack on the Wood. On the wood the fungus 

 may (1) attack and kill the spurs, (2) grow along the spur into 

 the shoot and form a spur canker, and (3) occasionally extend 

 considerably in the branch and kill extensive areas. An 

 example of an affected spur with a canker at its base is seen 

 in Fig. 2, whilst Fig 3 shows the killing of large areas of the 

 branch. The amount of canker which develops on the shoot 

 varies. In some cases the shoot may be only half girdled 

 (see Fig. 2), but in other instances the girdling may be com- 

 plete, in which case the portion of the branch above the canker 

 dies. The mycelium in the canker does not appear to spread 

 after the end of June, as the cankers do not increase in size 

 after that date. 



In Figs. 2 and 3 the grey spore-pustules of the fungus are 

 seen on the surface of the bark, having been pushed out by 

 the mycelium from within. Though the pustules develop 

 on the flowers soon after infection, they do not make their 

 appearance on the newly-killed spurs and shoots until the 

 winter. About December immature pustules may be found 

 bursting through the bark, which continue to increase in 

 number during the winter months. In spring they become 

 powdery in appearance, owing to the ripening of the spores, 

 and by the time the trees are in bloom they are liberating 

 spores in myriads. These are blown on to the opening flowers 

 and produce Blossom- Wilt. 



Method of Spread. As already explained, the disease 

 is spread by the spores of the fungus being blown on the open 

 flowers. It was found at Wye that the wilted trusses are far 

 more numerous in the vicinity of cankers and dead spurs 

 bearing spore-pustules, those trusses situated immediately 

 below such spurs or cankers being particularly liable to become 

 attacked with Blossom-Wilt. Thus, though infection through 

 spores carried by the wind from one tree to another or from 

 one plantation to another does to a certain extent take place, 

 the great majority of new attacks on any given tree arise from 

 spores produced by pustules on the same tree. The great 

 importance, therefore, of removing all wood which bears 

 pustules is obvious. 



Damp weather favours spore-production; and such weather 

 also retards the " setting " of the flowers and so keeps them 

 in a condition in which they are liable to become infected by 

 spores for a longer period. 



Varietal Susceptibility and Damage Caused, The 



varieties Lord Derby, Cox's Orange Pippin and James Grieve 

 are extremely susceptible, but, in addition, the disease occurs 

 on the following: Ecklinville Seedling, Duchess of Oldenburg/ 

 Worcester Pearmain, Allington Pippin, Early Julyan, Lane's 



