1919.^ ROOT DISEASE OF CACAO IN TRINIDAD. 193 



The directions here given as to treatment apply equally to limes and 

 to cacao, but as has been previously indicated, with the latter crop, so 

 far as the writer's experience goes, the cases are more usually of the 

 deep-seated kind, which does not permit of successful treatment. 



Control. 

 REMOVAL OF DISEASED TREES. When an infected tree is found it is 

 well that its destruction should be prompt, but it is an advantage to 

 choose a dry day for the operation. If the disease is so far advanced that 

 the fungus i^ producing conidia, either on the stem or on dead leaves and 

 twigs lying about, tlieii before it is distributed the spore-bearing surface 

 should be flamed witli a torch or by burning trash of some description 

 around them (Petch 1910). This disposes for th^ time being of the 

 means of aerial dispersal of the fungus, and removes what is otherwise 

 a real danger of the carriage of infection on the persons and implements 

 of the labourers. 



The diseased tree should be cut down, the stump dug out, and the 

 roots followed up and removed as completely as possible. One planter 

 gets out the fragments with a builders" sieve, and has had unusual 

 success with his supply plants. It is convenient for the labourers to 

 have baskets handy into which the small roots can be thrown as they 

 are dug out, otherwise they are in danger of being scattered. 



The diseased material should be destroyed by fire, preferably on the 

 spot. It has been formerly stated that the whole tree should be cut up 

 and burned, but I have recently satisfied myself that the necessity for 

 this, which h^s often been a real difficulty to planters trying to follow 

 instructions, may bo avoided. It is easy to see how far the fungus has 

 reached, and if the stem be cut above this point, and the top be disposed 

 of in such a way that it can dry out, it will not develop Rosellinia. 

 This has been verified on trees thrown into the edge of the forest, 

 provided they did not rest upon the ground, and on others perched on 

 large stumps and on rocks. It is better to dispose of even the stump 

 in some way than simply to leave it lying about as is too frequently 

 done, but all material actually infected certainly ought to be burned. 

 No material, root or stem, infected or uninfected, should be left lying 

 on the ground. In one instance the stem of a cacao tree, some 5 feet 

 long, which had been charred and thrown aside in the grass was found 

 sheeted from end to end with conidial fructifications, and stems and 

 branches of dead lime trees have been frequently seen, where they 

 have rested for some distance on or close to the ground, in a similar 

 condition. Had they been wedged among the branches of a tree they 

 would have been quite harmless. 



Under some conditions it may be necessary to choose a convenient 

 situation and carry to it the material to be burned, but such transporta- 

 tion has obvious dangers in the way of scattering bits of diseased 

 material. It should certainly be preceded by the scorching of any 

 spore-bearing surfaces. A kerosene blow-lamp is a useful appliance in 

 connexion with the scorching, and in starting fires. 



Treatment of the soil. — Attempts have naturally been made to 

 arrest the progress of the disease in the soil, or to sterilize situations 

 from which diseased trees have been removed, by the application of 



h 



