b 



1919.] BOOT DISEASE OF CACAO IN TRINIDAD. 189 



are very liable to occur. The comparative rarity of cases in the clearings 

 on thin soils is in keeping with the theory put forward that the original 

 sources of infection in any clearing are few in number. In poor 

 clearings the cases mostly remain restricted to these. Something may 

 be due however to the difference in the constitution of the original forest. 



In cacao plantations the conditions are usually more uniform, and 

 differences in the distribution of the disease are not well marked. There 

 is however a noticeable tendency for outbreaks to occur along the 

 course of ravines and on small enclosed alluvial flats. Among cacao, in 

 the situations so far studied, infection apart, from contact with stumps 

 or diseased trees, seems, as already remarked, to be relatively rare. 



COUNTER MEASURES. 

 Prevention. 

 In new lime clearings. It would be a counsel of perfection to 

 recommend the removal of stumps or even of logs from new clearings 

 in their earliest stages. In West Indian plantations such a policy is 

 not economically possible. But in arranging and planting new clear- 

 ing for orchard crops, the probability that root disease will occur should 

 be kept in mind, and certain precautions can be taken which will con- 

 siderably reduce the trouble to be faced when disease appears. 



First among these is provision for the construction, immediate or 

 when occasion and funds permit, of a complete and close system of 

 trench drains. To this end the arrangement of the trees should be 

 planned so that each block shall be isolated from the rest by main 

 drains and, where possible, each row separated from the next by a 

 trench. There will be many patches encumbered with logs and stumps 

 over which for some years the system will extend only in the plan, but 

 it is necessary to take long views, and too many cases have been seen 

 where, when the need for a trench has urgently arisen, the line has been 

 brought up against trees irregularly planted and now too valuable to be 

 destroyed. Drains ai'e being considered here, of course, not in view of 

 their primary function of removing water, but as isolation trenches 

 preventing the spread of root disease from tree to tree. At the same 

 time thorough drainage may be considered to have direct value from the 

 point of view of Rosellinia disease, for although, as has been pointed 

 out, the fungus does not thrive in water-logged soil, neither do the trees 

 and when that condition has been passed, the drier the soil can become 

 the quicker is the decay of organic matter and the less favourable the 

 conditions afforded to the fungus. 



It has been not uncommon in both lime and cacao fields when a 

 large stump has appeared to be a centre of disease, for a trench to be 

 dug around it cutting off the widely extending roots. When the fungus 

 has already got into the root system this measure usually comes too 

 late, but if it is applied to large stumps at the outset, especially to those 

 of susceptible species, it may be expected to have some success. 

 Possibly a variation recently suggested by A. Sharpies (1915), namely 

 the following out of each main root separately and removal of a section 

 where it gets down to about 2 feet from the surface, may have the 

 advantage over a trench that the cut ends are not left open to infection. 



