1919.\ BOOT DISEASE OF CACAO IN TRINIDAD. 197 



non-existent, or can be overcome. Like the preventive measures 

 already indicated, it should be applied first of all in the situations where 

 the losses are greatest, and extended as opportunity permits. 



It is not necessary, from the point of view of root disease that the 

 trenches should conduct water : indeeed, where loss of surface soil by 

 wash is feared more than the alternate danger of water-logging, it may 

 be advisable deliberately to check their function in this respect. They 

 may then be periodically cleaned out, and the deposit returned to the 

 soil. It gives a clearer point of view if the system is regarded as 

 one of permanent isolation trenches with a secondary function as 

 drains, rather than as one of drains in the first instance. 



lieturning to consideration of the treatment of infected spots, there 

 are two commonly existing situations which need to be dealt with. 

 These are (1) the case where a large patch of trees has already 

 been eaten out of a field, and the disease is spreading outward around 

 its circumference, and (2) the case where one or more trees have been 

 attacked around a large forest stump, infected or likely to become so, 

 which together with its heavy roots prevents the cutting of trenches 

 over an area which may include quite a number of trees. In both cases 

 the procedure has to be modified to suit each individual set of circum- 

 stances, but still follows the simple principles set out above. Where 

 roughly parallel main drains or watercourses exist on each side of the 

 area, they should be joined across above and below to establish an 

 outward limit, even though it may be a wide one, to the spread of the 

 infection. Then working inward from this, successive trees or rows of 

 trees which appear healthy may be separated off wherever it is possible 

 to dig a trench, and the disease thus confined to the narrowest limits. 



In the situations, sometimes met with, especially in cacao plan- 

 tations, where the trees are growing amongst a confusion of fallen 

 rocks, the possible measures are limited to early removal of so much of 

 an infected tree as can be got at, and the liming of the soil about adjacent 

 trees, with a view to preventing spore infections of the material which 

 accumulates in the enclosed pockets of soil. 



It has been commonly recommended that a trench be carried in a circle 

 around diseased trees and their contacts. This method has practical 

 disadvantages. The extent of the existing infection can never be ascer- 

 tained by inspection and a wide circle, while enclosing many healthy 

 trees may prove too narrow to include some line of infection that has 

 run off in advance of the general spread. A circle leads nowhere, 

 whereas a system of squares may be added to at any point and be 

 carried in any direction, and is capable of any sub-division. It has 

 moreover the great advantage of linking up with an existing or pro- 

 spective drainage system. 



As regards the form of the trench itself, there is but one essential so 

 far as root disease is concerned : that it should be deep enough to cut 

 through all the roots passing across its situation. When digging near an 

 infected tree, the earth removed should be thrown inward as a precaution 

 against the scattering of possibly diseased material among the healthy trees. 

 This refers more particularly to secondary trenches ; the outer trench should 



