238 DISEASES OF CROP-PLANTS 



Symptoms. 



Blossom blight : Small black spots due to fungus infection 

 appear in the open flower panicle, involving the death of groups 

 of flowers either directly or b}^ drying up the flower stalks. 

 The setting fruits are also frequently affected. The loss may 

 be small or may result in the complete stripping of the panicle, 

 according to the conditions prevailing. 



Leaf-spot : On the young leaves the fungus causes small 

 dark roundish or angular spots, usually i to 5 mm. in diameter. 

 They do not extend as the leaf grows older, but appear as 

 " shot-holes " in the otherwise healthy tissue. Care must be 

 taken to distinguish these from the injuries to both flower stalks 

 and young leaves due to infestations which may occur at this 

 stage with the larvae of a Cecidomyid fly. In the latter case 

 there are small swellings of the nature of galls. 



Fruit effects : On older fruits black spots of varied form, 

 which may be cracked or sunken, appear and may coalesce to 

 cover large areas. They penetrate deeply, and either cause the 

 rotting of the fruit on the tree or form centres of decay after the 

 fruit is picked. Streaking and russeting, affecting only the skin 

 of the fruit, are attributed to the arrested germination of spores 

 washed down upon the fruit from an affected twig or flower 

 stalk. 



Causative Fungus. 



The fungus is usually known as Gloeosporium Mangiferce Henn., 

 but it has been held to be identical with Colletotrichum glceo- 

 sporioides, best kno^vn in its connection with citrus tree diseases. 

 No description of the fungus adequate for its separation from 

 this and some other described members of the genus can be 

 given. 



Influence of External Conditions. 



The injury done by the disease is closely dependent on humi- 

 dity, the prevalence of rain or heavy dews at blossoming time 

 greatly increasing its incidence, and forming the principal factor 

 in determining the difference between a bad and a good mango 

 crop. 



Control. 



The disease can be controlled, and a heavier setting of fruit 

 secured even in normal seasons, by spraying with Bordeaux 

 mixture at frequent intervals during the blossoming period. 

 According to Rorer's experiments the fruit from sprayed trees 

 is cleaner and more attractive in appearance, and keeps much 

 better in storage or transit. 



