IGO FROGHOPPER BLIGHT OF SUGAR-CANE. 



It is shown that with excessive dryness both the froghopper and all 

 its enemies are domnant. so that no reduction in numbers will take 

 place. At a slightly higher grade of moisture the vermilion egg-parasite 

 is able to breed and reduce the number of eggs. A.t the third grade the 

 froghopper can breed and so outdistance the vermilion egg-parasite. At 

 a still higher humidity both the syrphid fly and the green muscardine 

 fungus come into play and reduce the froghopper, while the heaviest 

 rains do not affect the frogjiopper, but reduce its enemies and have an 

 injurious effect on the canes (p. 128). 



Size of Broods and Periodicity of attacks. There is no definite 

 relation between the size of the broods in one year. Sometimes the first 

 is the largest and sometimes the smallest. The second, is as a rule, 

 that by which most damage is caused. Frequently the third brood is 

 very small after a large and injurious second brood. More accurate 

 study of conditions may lead to an explanation of these facts (p. 1'29). 



No adequate explanation is available to explain the periodic recurrence 

 of severe blight at intervals of three or four years {see fig. 7). It is 

 possibly connected with the cycle of agricultural operations, (p. l.SO). 



The froghopper appears to have been more serious wi'hin the last 

 fifteen years than formerly. This is the case not only in Trinidad but 

 in other countries and with other insects besides froghoppers. It is not 

 considered that either the introduction of the ixiongoose or the develop- 

 ment of seedling canes are responsible for this increase. It is more 

 likely part of a wider influi-nce of the spread of civilisation, population, 

 a) id cultivation in a country' which has not yet worked out for itself 

 reliable rotational methods of agriculture to combat the disadvantages 

 inherent in Man's artificial method of planting large areas with the same 

 crop (p. 130). 



CONTROL. 



With tropical crops, and particularly with sugar-cane, methods of 

 prevention are more practicable with most pests than methods of cure. 

 With the froghopper the most important preventative consists of getting 

 the soil and the crop into such a condition that a less suitable environment 

 for the breeding of the froghoppers is produced. 



Soil Impkovemext. The drainage should be improved wherever 

 practicable ; on the fiat lands the drains should be run as close together 

 as is economically possible and they should be kept in working order 

 even on lands temporarily abandoned (p. 132). 



M.\NURING. Nearly all lands in Trinidad require more pen manure 

 and more lime. The shortage of labour should produce an increased 

 demand for animal cultivation and these animals will produce pen 

 manure. Artificial manures are best used in cases of blight only where 

 the land is good, but sufiering from an outbreak owing to temporary 

 unfavourableness of other conditions (p 133). 



Tillage. Every opportunity should be taken to improve the tilth 

 and depth of the surface soil by careful tillage. Fields should when 

 possible be laid out to correspond with soil changes so that the tillage 

 necessary for one part will not be injurious to the other (p. 133). 



Selection of Varikties. There is so little difference in resistance 

 between different varieties, with the exception of "Uba" and "Badilla", 

 that the planter, unless he is willing to grow one of these two, is 

 best guided in his choice bj' other circumstances than the prevention of 

 disease (p. 134). 



