364 [ THE PLUM 



DISEASES. 



By far the most common fungous disease is the plum 

 rust due to Puccinia Pruni-spinosae Pers. which some- 

 times provokes a very early denudation of the tree, with 

 the result that the fruit fails to develope properly and 

 its quality leaves much to be desired. Moreover the tree 

 is then apt to flower in autumn and when this happens 

 next year's crop may be seriously affected. The diseased 

 leaves develop small yellow or brownish pustules on both 

 surfaces of the leaf, but chiefly on the under surface. 

 Afterwards the whole leaf becomes dotted with yellow 

 spots and drops off. The disease recurs year and year, 

 but only affects the health of the tree and the quality of 

 the fruit when the attack commences early in summer 

 and the leaves are shed off too early. The development 

 of an attack seems to be closely connected with meteoro- 

 logical conditions and is unfortunately little amenable 

 to treatment. As a preventive measure the diseased 

 leaves may be collected and burned, and the soil tilled 

 deeply once or twice early in autumn. 



The mildew of the plum is a rare disease in our 

 orchards. It is due to Podosphaera tridactyla DBy. and 

 is characterised by the usual formation of white powdery 

 covering on the young leaves and twigs, which about 

 midsummer become dotted with minute black dots. The 

 disease is never frequent or troublesome, and is kept in 

 check by dusting with sulphur, or by spraying with a 

 solution of sulphide of potash or even with Bordeaux 

 mixture. The shot-hole fungus Cercospora circumsassa 

 Sacc. is rarely seen on the plum. To Exoascus deformans 

 Fckl. is due the production of the so-called witches' 

 brooms: the affected branch developes a dense growth of 

 small slender twigs with small and usually deformed 

 leaves, and is unproductive. These witches' brooms 

 should be cut back and burned, but they have been 

 noticed here only on a few occasions. Another species 



