1919. \ INVESTIGATION OF FBOGHOPPEB PEST, dx. 65 



37. The first effect of any adverse condition, it has been shown, is to 

 afford an opportunity for the development of root disease; the methods 

 of Trinidad agriculture, it has been further shown, ensure the presence 

 of sufficient root fungus in the fields to take advantage of the opportu- 

 nity. When a field attacked by froghopper is already in some degree 

 infested with root disease, or when it becomes so infested in consequence 

 of the effects of froghopper attack, (as these effects are developed 

 when conditions are already dubious) the permanence of the result is 

 adequately accounted for. Such fields will pass into the condition of 

 blight as I saw it. 



38. This conclusion does not carry with it the assumption that all 

 blight is caused in the same wa_y. The final condition is one of infestation 

 with root disease, and a condition as severe as any existing in Trinidad 

 can and does occur where froghoppers are unknown. In the production 

 of many of the examples I saw, and especially of those in which the 

 damage was most intense, there was no necessity to assume that the 

 insect had taken any effective part. 



KE MEDIAL MEASURES. 



39. There remain for consideration the nature and application of the 



agricultural practices which, according to the view of the situation put 



forward, will serve to reduce the injury directly caused by froghopper 



and prevent the infestation of fields with root disease. No general 



prescription can be offered. Each estate, and each varying section of 



an estate, will need to be considered separately, and modifications in 



prevailing practice be made to the extent which consideration p,nd 



experience show to be necessary in each case. The manager of the 



estate, if he studies his fields, is commonly in the best position to 



decide concerning these and where more critical comparisons are 



necessary they can only be supplied by experiments conducted under 



scientific control. 



Sanitation. 



40. As regards methods of cropping, the possible variations may be' 

 arranged in an ascending scale, beginning from the system of continuous 

 cropping previously described. The departures from this may be 

 regarded in the character of sanitary measures, the object of which is to 

 rid the fields, to the degree found necessary, of vegetable material in the 

 soil which carries on the existence of root fungus. This end is attained 

 in the breaking down of such material and its assimilation by the soil. 



41. The first and simplest of these measures comes within the period 

 between the reaping of one crop and the planting of the next, and 

 consists in thorough preparation of the ground. Early ploughing-out of 

 the stools, and the subsequent working of the land so that they 

 are broken up and rotted, will usually suffice for their disposition. 

 "Where circumstances do not allow of this being done in time they may 

 be collected and rotted down in heaps. Burning I do not advise because 

 of the loss of organic matter entailed. 



42. Ther-e is a good deal of land, which it will be understood is that 

 which approaches the best in quality, on which thorough treatment of 

 this kind combined with adequate manuring and cultivation may be 

 expected to supply the necessary margin of safety, and I am inclined to 



