198 TRINIDAD AND TOBAGO BULLETIN. [XVIIl. 4. 



be put far enough away to aA-oid, in general, the chance of finding such 

 material. The earth should be distributed, not banked at the edge of 

 the trench, unless put there in exceptional circumstances with the 

 express purpose of avoiding wash. Under no circumstances, however, 

 should the collar of the tree be earthed up. Roots passing into the 

 healthy area should be followed up and removed, so far as this can be 

 done without much injury to other roots. It would be well if cut ends 

 of roots were painted. 



Survival of supply plants. — On the thoroughness with which the 

 clearing up is done depends the chance of survival of an early supply 

 plant. It has been found in St. Lucia, where the results of several 

 years of experience of the treatment of this disease on cacao are now 

 available, that where the work has been carried out under the personal 

 supervision of the planter, supplies put in a month afterwards have 

 remained healthy. The longer the delay the greater the chance of 

 survival. It must be remembered that a supply may do well for a few 

 months while its roots occupy the site from which the stump was 

 removed, and then become infected from some outlying fragment of the 

 old tree as its roots spread wider. Such cases have been definitely 

 traced. 



The Possibilities of Control. 



Rosellinia disease in orchard cultivations is by its nature capable of 

 the most serious consequences. It is cumulative in its effects: each 

 tree that contracts it infects as a rule not merely one but several more, 

 and each tree killed takes at least five or six years to replace. In new 

 clearings, encumbered with stumps and logs, and in cacao fields with 

 large shade trees, the disease is difficult to deal with. 



It may be confidently claimed, however, that the application of the 

 principles of prevention and control set out in the preceding pages will 

 reduce the annual losses to a minimum that is not likely to be serious, 

 and one may further expect a gradual diminution year by year of even 

 the sporadic cases. 



Control does not depend on any special apparatus or material, but 

 on operations of a familiar type, demanding little special skill. Every- 

 thing depends on the vigilance and thoroughness with which they are 

 carried out. Careless or half-hearted work is of little use against this 

 disease, which is apt to pursue its course with an appearance of delibera- 

 tion and inevitability which is disconcerting. 



SUMMARY. 



Several species of the genus Rosellinia give rise to a well-defined 

 type of root disease in numerous countries of the world, temperate and 

 tropical. The fungus kills out cultivated trees or shrubs in patches, and 

 often infests the soil and destroys practically all vegetation with which 

 it comes into contact. 



