194 TEINIDAD AND TOBAGO BULLETIN. \XVIIL 4. 



disinfectants to the yoil. In cacao plantations in these islands lime has 

 been frequently used, and, in Grenada especially, iron sulphate. One 

 planter at least has used sulphur. So many factors are involved, and 

 the circumstances are so variable that one cannot say what the actual 

 effect of these applications has been. 



Fawcett (1915) has experimented with lime, sulphur, chloronaphtho- 

 Ifcum, copper sulphate, potassium permanganate, and potassium 

 bisulphite. Plots which received in the one case lime and in the other 

 sulphur at the rate of 500 grams per square metre showed no losses in 

 three years, as compared with 6 per cent, of loss in a check plot, and 

 3 per cent, in a plot receiving about one-fourth the amount of sulphur, 

 and another to which chloronaphtholeum was applied at the rate of about 

 50 c.c. per square metre. It was found that the last named substance 

 was ineffective unless used in amounts involving a prohibitive expense. 

 Spraying the surface of the soil with copper sulphate solution equivalent 

 to 25 grams of the salt per square metre was sufficient to check and 

 apparently exterminate the fun.u;us in the soil of a small diseased plot. 



Bernard (1909) qviotes from Raciborski a method which he regards 

 as having been successful against root disease of tea. It consist in 

 working up the soil with quicklime and then watering it with a 10 to 15 

 per cent, solution of sulphate of ammonia ; the idea being that ammonia 

 is liberated in sufficient quantity to disinfect the soil. 



Bordaz (1914) has claimed very successful results in Martinique from 

 the use of carbon bisulphide emulsion. Trials of this substance in 

 Dominica have failed to demonstrate its usefulness against root disease, 

 although it has given apparently good results used against soil grubs. 



For my own part I cannot ?ee that there is much scope for the use 

 of disinfectants in the control of this disease. It is safe to say that at 

 the present time there is no disinfectant available which is cheap 

 enough to be used in sufficient quantity to sterilize any considerable area 

 of ground. When we are dealing with a fungus which penetrates to 

 every part of even the thickest roots, it cannot be expected that 

 chemical agents will kill it out, or, being necessarily of a transient 

 nature, stop its progress, unless all woody \naterial is removed. When 

 this has been done, exposure of the soil to sun and air is probably just 

 as effective as any disinfectant could be. Where it is required to deal 

 with infested soil or accumulations of vegetable matter under shade, as 

 for example in the case of the lime trees with surface infections 

 specified above, it is better to scrape away the surface soil with a hoe 

 than merely to extinguish the fungus with a disinfectant, leaving 

 material liable to reinfection. Such a scraping of the soil combined 

 with removal of low branches and of any other hindrances to the free 

 circulation of air, has in the cases under my observation been 

 sufficient. An application of lime, of sulphur, or according to Fawcett's 

 results, of copper sulphate solution, would give an additional margin 

 of safety. 



The addition of lime to the soil when clearing up a spot from which 

 infected trees have been removed is commonly practised, and is believed 

 to contribute to success in establishing supplies. It seems to me 

 probable that the results obtained are not so much due to the sterilizing 

 effect of the lime as to its action in hastening the disappearance of 



