■SECTION VIII. — FACTORS INFM'EXCING BLIGHT PRKVAF-KNCK. 113 



Soils in such a condition are not suitable for the growth of the soil 

 bacteria which cause decay, and until they are properly turned over and 

 cultivated, cane trash or even pen manure may be seen in compact 

 masses in the ground, not decaying to form the humus that is so essential 

 for the impi-ovement of the soil and the supply of organic plant food. 



It is not only in Trinidad that the close relation between soil 

 ■conditions and froghopper blight has been noticed. 



In his report on the Blight in Mexico Urich (Bull. Dept. Agr. XL 

 No. 71, p. 298) says "on the plantation where I was the froghoppers 

 occurred under exactly the same conditions as here [Trinidad] viz : — on 

 low-lying damp ground they weie numerous on cane and grass, becoming 

 less on porous and friable soils." 



In the outbreak in British Guiana in 1918 both Bodkin and Moore 

 emphasised the importance of soil conditions. Bodkin (1918 B.) 

 mentioned the water logged condition of the soil aggravated by the 

 injurious effect of the use of nitrate of soda, and Moore (1919) says 

 "When the soil was stiff the insects tended to be more numerous." "At 

 Plantation Ogle .... the canes showed distinct evidence that they had 

 been contending against an excessively moist, cold, stiff clay, and it was 

 these soil conditions which primiril3' induced the froghopper attack." 



TEMPERATURE. 



The daily and annual variation of temperature in Trinidad is not 

 great, nor have we any evidence that ifi in any way affects the prevalence 

 of bligiit. Attention is drawn t ) it here chiefly in view of the recent 

 work of Johnston and Hartman (1919) on the root rot of tobacco, where 

 soil temperature had been found to be the niDst important factor in the 

 environment (see -p. 94). If temperature had any similar effect on the 

 root disease of sugar-cane in Trinidad, it would assume a much greater 

 importance. Further work in this direction is desirable. 



DRAINAGE. 



In view of what has been said above of the influence of rainfall and 

 soil conditions on the prevalence of l)light, it will be expected that 

 drainage is an important factor. 



Drainage in Trinidad has to serve the double purpose of (1) rapidly 

 removing surface water in heavy downpours, (2) slowly removing the 

 percolating moisture so as to aerate the soil. 



In one field in the Naparimas, where froghoppers had been persistent 

 for man}' years, the beds and the sides of the drains on part of it were 

 forked in September 1918 to allow the moisture to percolate better into 

 the drains. In the following year the froghoppers and consequent blight 

 were much less serious on the part that had been forked than on the 

 unforked part. This case is confused by the effect that the forking 

 would have on the aeration of the soil, but there is little doubt that both 

 contributed to the final beneficial result. 



Until the last ten years or so all the cane plants in Trinidad were 

 set in I'ows across the beds so that drainage was rapid. With 

 the introduction of implemental tillage large areas are gradually being 

 relaid with long beds in which the rows of cane are parallel to the drains. 

 Drainage, unless helped by well planned tillage, is not so good on beds 

 so laid out, and it may be necessary on some lands to reduce the distance 

 between the drains. 



