122 DISEASES OF TROPICAL PLANTS OH . 



occur in Cuba, but if so, it is no doubt frequently 

 confused with a dieback which is due to grubs and 

 drought. It attacks citrus trees of all varieties and ages ; 

 The diseased trees make an exceptionally vigorous 

 growth early in the season and produce a number of deep 

 green coloured water sprouts. This condition is followed 

 by a characteristic dying back of the tips, formation of 

 rusty spots on the leaves and twigs, and multiplication 

 of buds in the leaf axils, and frequently the formation 

 of more or less gum. The leaves may fall or may hang 

 on the tree indefinitely. When bearing trees are suffer- 

 ing from this disease, the fruits begin to fall when about 

 one-third grown. This premature falling is accompanied 

 by a lighter colour, followed by reddish brown specking 

 or irregular blotching and splitting of the fruits. Gum 

 is also formed either on the surface or in the core. 



This appears to be a physiological disease which 

 may be due to an excess of ammonia in the soil or 

 fertilizers, to improper soils, to poor drainage, or to an 

 underlying impervious soil. The treatment must be 

 in accordance with the conditions causing the trouble. 

 Some of the more recent but unpublished studies on this 

 disease indicate that it may be a form of gummosis. 



Other parasitic fungi, which have been reported as 

 of some economic importance, on the citrus fruits, are 

 Diplodia aurantii, Catt. , and Pleospora hesperidearum, 

 Catt. ; Septoria limoriam, Passe., and S. sicula, Penz., 

 on ripe fruits in Italy. 



Orange Tree Canker. This disease, which is due to 

 Didymella citri, Noack, attacks the branches, causing 

 depressions of the bark followed by longitudinal and 

 transverse cracks with thickened margins. The black 

 pycnidia are produced within these wounds. The 

 disease has been reported from Brazil. 



Sooty Mould. This trouble is due to a fungus known 

 as Capnodium citricolum, M'Alpine, 1 which occurs in 

 the southern part of the United States, California. 



1 This disease has been described as due to Meliola camelliae, (Catt.) Sacc., but 

 more recent studies indicate that it should be placed in the genus Capnodium. 



