II 



COCOA DISEASES. II. 



In the December Bulletin (page 270) an account was given of a 

 disease of Cocoa pods in which the darkening of the pod is 

 accompanied by white mould on the outside. 



Mr. Hart in a paper on " Some Fungi of the Cacao Tree* states 

 that in Trinidad "the disease was observed to be most prevalent 

 in places where the atmosphere was humid and where the pods 

 had been allowed to rot beneath the trees." 



Mr. Albert Howard, formerly the expert in fungoid diseases to 

 the Imperial Department of Agriculture, recommends, f besides 

 the remedies mentioned last month, " Reduction of shade. Where 

 cacao is grown under shade as in Trinidad, and where this dis- 

 ease is prevalent, it would be advisable to diminish the number 

 of shade trees and to prune the cacao trees as much as possible, so 

 as to considerably reduce the humidity of the atmosphere. In this 

 way conditions could be adjusted so as to be unfavourable to the 

 development and spread of the fungus while not interfering with 

 the growth of the cacao tree." 



Another disease has been noticed as occurring in Jamaica, that 

 known as the " brown rot" disease of the pod. J This was deter- 

 mined here, and confirmed by reference to the Commissioner of 

 the Imperial Department of Agriculture. It is described in the 

 paper by Mr. Howard as follows — 



" When cacao pods are attacked by this disease, a circular 

 brown patch makes its appearance which gradually extends all over 

 the pod and causes complete destruction of the rind and its con- 

 tents. The time taken in the destruction of a pod varies somewhat 

 according to its ripeness, but usually falls between six and ten 

 days from the appearance of a diseased spot visible to the naked 

 eye. This appearance must not be confused with the rusty or 

 " mahogany" pods which result from " thrips" when the whole of 

 the outside of the pods takes on a rusty colour but when the rind 

 is not diseased.** The definite brown patches in question gene- 

 rally commence either at the insertion of the stalk or at the free 

 end of the pod, but they may occur at other points, especially 

 where the rind has been injured or where the pod comes in contact 

 with a branch. These diseased pods are particularly numerous 

 near the '" breaking-grounds" where the beans are extracted by 

 the pickers. If one of these attacked pods is carefully examined 

 it will be found that the brown area is rotten and that the decay 

 extends to and spreads round the shell of the pod to a much 

 greater distance than would be supposed from a surface examina- 

 tion. The disease soon spreads to the " beans" which are speedily 

 attacked and destroyed by a greyish fungus mycelium which grows 



* W. Indian Bulletin Vol. I. pp. 4l>2-7 with plate, 



t W. Indian Bulletin Vol. II. p. 198. 



j Diplodia cacaoicoia. 



** The rusty colour of the pods attacked by "thrips" is caused by the formation of a 

 cork layer, below thn epidermis, which cuts ofE all the cells above it. These cut off cells 

 consequently dry up and turn brown. The cork layer is really a new epidermis layer 

 formed on account of the numerous perforations made in the original epidermal cells 

 by the " thrips." 



