SECITION Vril. — FACTORS INFLUEXCING BLIGHT PREVALENCE. 121 



In 1918 and 1910 this insect was again common, particularly in 

 blighted fields, but whether this was accidental or not is impossible to say. 



The caterpillars of the small moth borer {Diatrcea sy;^j.) are also 

 common in the cane fields in Trinidad and do more injury than is 

 usually attributed to them. They arc frequently found in blighted fields 

 but the probable position with regard to both these borers is that they 

 weaken the cane and make it less able to withstand the blight, but do 

 not in any way render the cane actually more attractive to the frog- 

 hopper. 



PREVIOUS DAMAGE AND SOURCE OF PLANTS. 



There are certain districts and fields in the island that have shown 

 themselves to be more liable than others to blight, but at the same time 

 a field badly damaged one year may be quite free in the following year. 

 This is no doubt due to the fact that some of the environmental factors 

 are more or less constant (soil, drainage, contour) while others change 

 from year to year (rainfall, age of cane, agricultural processes). 



One field at &olconda Estate was severely damaged as plant canes 

 in 1917, almost free from damage as first ratoons in 1918 and again 

 badly damaged as second ratoons in 1919. 



At Esperanza six out of eight fields badly damaged in 1913 had been 

 previously damaged in 1912. Five new fields were slightly damaged in 

 191.3 and they were all near fields affected in 1912 (Urich Bull. Dejit. 

 Agric. XII p. 203.) 



On the Government Pond field at Hermitage blight has occurred for 

 three successive years in the same part of the field. 



At Caroni the fields affected in 1918 were in the same area as those 

 damaged in 1917. 



At Breehin Castle a field was badly damaged in 1903 and has never 

 since had any injury Avhatever. 



Many other examples could be given, but the conclusion is that on 

 the whole damage is more likely to occur in fields that have been 

 recently damaged than in others (allowing for the beneficial effect of 

 replanting fields that have been in old ratoons). 



In the same way plants taken from a damaged field are more likely 

 to carr^' with them eggs of the froghopper and traces of root fungi than 

 those from healthy fields, and as far as possible only the latter should 

 be used. 



