1144 WlTHER-TlP AND BROWN BoT OF PLUMS. [M*B. 



The severity of Wither-Tip is greater in some seasons than 

 in others. W et. cold weather in spring favours its development,, 

 but since epidemics of Wither-Tip have been found to correspond 

 with severe attacks of aphis, it is possible there may be a con- 

 nection between them. The aphides, by puncturing the leaves, 

 would injure the tissues, and render them particularly susceptible 

 to invasion by the fungus mycelium. 



Brown Rot on Fruit.— The fruit is more often attacked when 

 approaching maturity, the slightest wound or bruise allowing 

 the spores to penetrate and bring about infection. Once it has 

 gained an entrance the mvcelium rapidly destroys the fruit, and 

 finally reduces it to the hard, wrinkled structure known as a 

 " mummy." The mummies may fall to the ground, but usually 

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

 of two or three by means of the fungus mycelium (Fig. 5). 



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

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

 infected by direct contact with mummies or with other diseased 

 fruit (Fig. 6), 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 mvriads of spores, and thus bring about 

 new attacks of Blossom-Wilt and Wither-Tip. 



Varietal Susceptibility. — With regard to Blossom-Wilt and 

 Wither-Tip. as a general rule Victoria and Czar Plums surfer 

 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 subsequently killed. 

 Occasionally Monarch Plums suffer more exteusively than either 

 of the above. Pond's Seedling and Biver'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. 



* It may hp noted that Appl^ B>-o\vn Rot (M. fructiqma) which is 

 distinguished by its huff instead of grey pustules, is sometimes found on 

 ripe plunifl causing a rot. It appears-, however,- to be confined to such fruit 

 and not to attack flowers or shoots. 



