1919.] INVEST IGATIOX OF FROGHOFPER PEST, dc. 61 



THE FACTORS INFLUENCING ROOT DISEASE. 



15. In soil which is in good tilth and well-drained, so that roots 

 develop freel.y and penetrate deeply, root fungus may be present in 

 abundance about the stools of plants orratoons and, provided the rainfall 

 is not markedly deficient, do no visible harm. This in fact appears to be 

 the regular state of affairs on much of the cane cultivation of Trinidad, 

 where, at least in the Naparimas, it seems to be a quite general custom 

 to plant between the old rows and, much later on, to divide the 

 bank and turn the stools, full of root fungus, over on to the rows of 

 young plants. 



16. That this system can in so man-y cases be practised with impunity 

 is the most convincing testimony that could be adduced as to the 

 suitability of natural conditions in Trinidad for cane cultivation. Its 

 practice involves the assumption that no unfavourable circumstance will 

 occur to give the fungus an opportunity of becoming harmful. The 

 position of the cane plant under these circumstances is that of a man in 

 an unsanitary town depending upon the maintenance of his vigour to 

 keep him free from infection. 



17. "Where this system of planting is associated with continuous 

 cropping, long ratooning, and the practice of replanting during crop, so 

 that no break of annual production occurs, we have the most extreme 

 form of sugar-cane agriculture obtaining in these islands ; one in which 

 root disease, as a factor, is practically left out of consideration. Where 

 it can be carried on with success, as it seems to be on the best parts of 

 several estates I visited, I do not see that any theoretical considerations 

 need be allowed to interfere with its continuation. 



18. From this extreme there is, in the West Indies generally, a long 

 series of gradations in agricultural practice corresponding to various 

 degrees of disability of soil or climate, until the opposite extreme is 

 reached, as in the more arid districts of Barbados, in which plant canes 

 only can be grown and these have to be alternated every third, or even 

 in some cases every second, period with a different crop, in addition to 

 the land being thoroughly prepared well ahead of each planting season. 



19. The governing factor in all these variations, according to my view 

 of the matter, is the increasing necessity, as conditions grow less 

 favourable, of reducing by preparation and rotation the amount of root 

 fungus to which the plants are exposed, and also reducing, by curtailing 

 ratoons, the period of exposui-e to the fungus which accumulates on 

 the stools. 



20. Discussion of the most general of the unfavourable conditions 

 referred to can be grouped under considerations of soil and climate. 



Soil Conditioxs. 

 The physical condition of the soil mainly has effect, as previously 

 mentioned, in its influence on free and deep rooting. On many of 

 the blighted areas, or areas subject to blight, which I visited in 

 Trinidad, there was a conspicuous deficiency in tilth, and this in 

 my opinion, is mainly due to an insufficiency of organic matter 

 in the soil. Sugar cane is not an exhausting crop. It supplies in 

 trash, and in its contribution of fodder to the formation of pen manure, 

 a liberal amount of bulky material to be restored to the soil, and the 



