1921.] Wither- Tip and Brown Eot of Plums. 1143 



shoots. Trees which have suffered from Blossom- Wilt may he 

 recognised by the brown, withered leaves which usually remain 

 attached instead of falling off. 



The damage caused by Blossom-Wilt is very serious in certain 

 seasons. The factors chiefly contributing to an epidemic attack 

 are a low temperature, and a very moist atmosphere during the 

 flowering period. The former retards the development of the 

 flowers, and causes them to remain susceptible to infection for 

 a longer period than usual, and the latter favours the production, 

 by means of the pustules on mummied fruit and dead wood, of 

 an abundance of spores. 



Wither-Tip. — In Wlther-Tip the fungus attacks the young 

 green shoots and causes them to die-back. In this way many 

 of the leading shoots are killed, and the buds at the base are 

 then stimulated to precocious development, and instead of fruit 

 buds, a number of weak, ill-ripened shoots are produced. 



The Wither-Tip form arises from spores formed on the spore- 

 pustules on mummies, on wood attacked the previous season, 

 and probably also from flowers killed by Blossom- Wilt. It usually 

 appears about the end of April or the beginning of May, when 

 some of the young shoots may be seen to wither. The wilt- 

 does not always begin at the tip of the shoot ; it may commence 

 some distance down, the fungus in this case entering at a node 

 or through a leaf. In Figure 3, the dark portion of the shoot 

 shows the infected area, the fungus having gained infection 

 through the leaf on the left. Shoots attacked by Wither-Tip 

 hang downwards ; at first thev are flaccid, but later the tissues 

 harden and dry, and the dead shoots may be recognised by the 

 characteristic curve. The dead brown leaves, being killed pre- 

 maturely, do not usually fall from the tree, but hang on during 

 winter and even until spring (Fig. 4). When it is a spur that 

 is invaded the fungus sometimes forms a canker similar to that 

 formed in apples. 



Spore-pustules develop during the following winter and spring, 

 on all the shoots and spurs which have been killed (Fig. 4, 

 specimen to left), and these give off spores which provide for 

 the fresh infection in spring. The pustules are small and grey 

 in colour, they commence to show in December, and increase in 

 number as spring advances. Large quantities of spores are 

 liberated in March, April and May. The fungus in dead twigs 

 may retain its vitality for more than one season, and liberate 

 a crop of spores during the second winter after attack. The 

 importance, therefore, of removing such shoots is obvious. 



