i88 DISEASES OF CROP-PLANTS 



formation has been secured regarding the manner of distribution 

 of the fungus ; strong winds may detach and transfer fragments 

 of mycelium, and scavenging insects and birds may carry these 

 or spores from one tree to another ; it is not thought that transfer 

 by the pickers is of much account. 



Control. 



Attempts have been made to prevent infection by appHcations 

 of mixtures of slaked lime and copper sulphate, Bordeaux paste 

 and mixture, lime and salt, and rock salt. The results are so 

 far inconclusive though good effects are believed to have been 

 obtained in some instances. 



The early eradication of diseased trees, when thoroughly 

 carried out, has been effective with this as with other types of 

 bud-rot. 



Leaf-stalk Rot caused by Phytophthora parasitica. 

 Symptoms. 



S. F. Ashby has described a disease of coconut palms occurring 

 in Jamaica in which the earliest symptom is usually a yellowing 

 and withering of the tip of a leaf on the outside of the crown. 

 The affection spreads to adjoining leaves and finally most of the 

 outer leaves break down. Progress is slow and typically the 

 bud is not affected. The bunches of nuts fall owing to the 

 removal of the support given them by the leaves, but have not 

 been seen to be infected. 



The stalks of the leaves attacked show dark brown somewhat 

 sunken spots, from one to several inches in diameter, on the 

 upper and under surfaces ; the lowest spots are usually situated 

 several inches above the junction with the stem. Long dark 

 patches are also frequently present on the limbs, and gum may 

 exude when the affected areas crack. Internally the spots and 

 patches show either a sodden rot with a narrow red margin or 

 are light to dark brown, depending on their age ; frequently 

 they pierce entirely through the limb. 



Incidence. 



The disease has been so far met with in Jamaica only on 

 three neighbouring estates in a district of high rainfall. Cases 

 have occurred in trees from ten to fifteen years of age, but in the 

 greatest number on trees of five years beginning to bear. 



The Causative Fungus. 



The tissue of young spots is penetrated by the stout sparingly 

 septate intercellular mycelium of a Phytophthora, with few 

 branches entering the cells. In older spots the hypha; show more 

 frequent septation and grow through the cells. Felts and webs 

 have not been found on the surface of the spots. 



