39 



they remain on the tree until spring, stuck together in groups 

 of two or three by means of the fungus mycelium (Fig. 1). 



Although it is on ripe or nearly ripe fruit that Brown Rot is 

 best known, it may also attack young fruits. These may be 

 infected by direct contact with mummies or with other diseased 

 fruit, but apart from this it is clear that wounds or abrasions 

 of the surface are necessary for infection. Soon after the 

 fruits are infected, small grey spore-pustules appear, often in 

 concentric rings.* The spores liberated from these pustules 

 infect other fruits. When the fruit is destroyed, and the dry 

 mummy stage is reached, the pustules for the most part cease 

 forming spores and remain dormant till spring, when they 

 regain their activity, liberate myriads of spores, and thus bring 

 about new attacks on the flowers, shoots, and fruits. 



Varietal Susceptibility. With regard to Blossom- Wilt 

 and Wither-Tip, as a general rule, Victoria and Czar Plums 

 suffer most. In 1920 the attack on these varieties in East 

 Anglia was particularly severe, and it was estimated that 80 per 

 cent, of the flowers and shoots were killed in certain districts. 

 Later in the season the trees, made new growth, but this was 

 very weak, and on Victoria especially much of it was sub- 

 sequently killed. Occasionally Monarch Plums suffer more 

 extensively than either of the above. Pond's Seedling and 

 River's Early are not usually so severely attacked. 



The fruit-rot form is common on all varieties, although if 

 trees are extensively affected with Blossom-Wilt and Wither- 

 Tip the likelihood of the fruit becoming attacked by Brown Rot 

 is greater. 



Measures of Control. At present there are three methods 

 of treatment, as indicated below: 



1. Removal of affected fruits and mummies. It cannot be 

 understood too clearly that new infections are mainly brought 

 about by the mummies hanging on the trees, and by diseased 

 twigs. Diseased and decayed plums should therefore be picked 

 and dropped to the ground at the same time as the crop is 

 gathered. Any mummies that are left on the tree should be 

 removed in winter before the buds swell. They should be col- 

 lected and burned or deeply buried. 



2. Cutting out of diseased shoots. As far as possible all 

 dead twigs bearing pustules should be cut out. If the attack is 

 not extensive it will be possible to do this without excessive 

 labour or serious injury to the trees. When large areas are 

 concerned the labour is of course prohibitive, and the trees may 

 be injured through excessive cutting out. At the same time, it 

 should be remembered that the affected wood is quite dead, and 

 therefore useless. 



* It may be noted that Apple Brown Hot (M. fructigena) which is 

 distinguished by its buff instead of grey pustules, is sometimes found 

 on ripe plums causing a rot. It appears, however, to be confined to 

 such fruit and not to attack flowers or shoots. 



