242 COCOA CHAP. 



(1) Insecticides with which the leaves are treated 

 and which poison the insects when they eat the leaves 

 (" stomach poisons "). Formerly Paris green was much 

 used for the purpose, but nowadays arsenate of lead 

 is considered to be preferable. Arsenate of lead is 

 sprayed on the leaves in the proportion of 1 part to 100 

 parts of water, or even 1 part to 1000 parts of water. 

 As the cocoa does not suffer much from leaf-eating 

 insects, spraying of the whole tree with this solution is 

 rarely necessary. It is sometimes useful in the case of 

 a sudden attack of leaf-eating caterpillars, and it has 

 been tried in the fight against borers. 



(2) Insecticides which kill the insects on coming 

 into contact with them (" contact poisons "). This group 

 contains the numerous mixtures used against lice, scale 

 insects, mites, etc. Kerosene emulsion has been reported 

 to be successful against thrips in cocoa. It is prepared 

 as follows : 2 parts of water and 1 part of soft soap 

 are mixed and heated till the mixture boils and the 

 soap is wholly dissolved ; then it is taken from the fire 

 and 4 parts of kerosene are added, and the mixture is 

 thoroughly mixed for ten minutes by means of a sprayer. 

 This mixture is kept as a stock solution before use, and 

 is diluted to ten or twenty times its original volume. 



A great many other contact poisons have been used, 

 especially against scale insects, and it is not impossible 

 that one will be found to be effective against Helopeltis. 



(3) Insecticides which kill the insects by intoxica- 

 tion. Carbon bisulphide and carbon tetrachloride are 

 the important representatives of this group. Carbon 

 bisulphide is used against the larvae of borers ; it is 

 injected into the tunnels by means of a small syringe. 



FUNGUS DISEASES 



Root diseases. These diseases of the root occur in 

 many countries, but most of them do comparatively 

 little harm, and have not yet been the subject of 

 thorough investigation. 



