18 TBINIDAD AND TOBAGO BULLETIN. [XIX. I. 



disparity that occurs, in the amount of damage consequent upon an 

 infestation, appears to be sufificiently accounted for by the differing 

 Tjowers of resistance already explained. 



32. The number of the factors involved is so large, and their outcome 

 so often apparently contradictory, that only the patient correlation of 

 ■evidence collected over a long period can provide definite knowledge 

 concerning their individual effects and mode of action. The conclusions 

 so far reached are general in their nature, but are believed to afford a 

 sound basis for the recommendations as to agricultural practice 

 put forward. 



33. The measures prescribed have application against both root 

 disease and froghopper, their effect in both cases being to increase the 

 resistance of the plant and to make conditions less favourable for the 

 carrying over and propagation of the parasite. They consist of the 

 reduction in certain cases of the ratooning period, the maintenance of 

 a high standard of preparation, cultivation, and drainage, the liberal 

 use of organic manures, the application of a iequate amounts of lime, 

 and the practice of regular rotation of croj^s, matters which were 

 ■discussed in detail in my previous report. 



34. There is one practice which cannot be too often or too severely 

 •condemned from the point of view of pests and diseases, that of throw- 

 ing out fields to grass, which crop being closely related to sugar-cane, 

 harbours both root fungus and froghopper and does not afford the benefits 

 •of rotation. The matter is made worse when, as usually happens, the 

 ■old cane stools persist and send up a crop of debilitated shoots. The 

 stools in fields intended to be rested should be ploughed out, and it 

 ought not to be difficult, with some initial cultivation, to establish a 

 green crop which will protect the soil and maintain itself against grass 

 and other weeds. 



January 21, 1920. 



