CHAPTER XI 



DISEASES 



For the cocoa planter to adopt preventive or combative 

 measures in an intelligent manner against the various 

 pests to which cocoa is subject, it is necessary that he 

 should acquire a knowledge of the principles of phyto- 

 pathology, which involves an understanding of the 

 symptoms, causes, and the life history of plant diseases. 



In attempting a diagnosis of plant diseases it is import- 

 ant that he should be able to differentiate between 

 symptoms due to the action of organisms and those due 

 to environment. For example, a discoloration of the 

 foliage may have been caused either by fungus mycelium 

 present in the internal structure of the leaf or by excessive 

 moisture at the roots of the tree. The therapeutic 

 measures to apply to the former ailment would obviously 

 have to differ widely from those applicable to the latter. 



The etiology or causes of plant disease may be included 

 in two main groups ; the first is associated with its inani- 

 mate environment, such as soil, light, atmosphere, or 

 temperature, while the second is connected with the 

 work of living organisms, such as plants and animals. It 

 is necessary to point out, however, that the effects of 

 the work of the living organisms are influenced by the 

 inanimate environment as well as by the host plant. 

 A plant growing under satisfactory conditions as regards 

 soil and climate is better equipped to withstand disease 

 than one growing in a sour or water-logged soU, or one 

 growing in an unsuitable temperature. 



In the case of the cocoa tree too dense shade predis- 

 poses it to fungus disease. A lack of nutriment in the 

 soil, constricted root or foliage space, may likewise be 

 placed in this category. A definition of disease as affect- 



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