120 FROGIIOPPER BLlGll'l OF SUGAR-CANE. 



I was informed by one planter that the recent outbreaks of blight 

 were due to the replacing of tlie old deep-rooting Bourbon cane by 

 shallower rooted seedlings. Kut Mr. J. R. Bovell assured me that the 

 old Bourbon cane was shallow rooted and my own observations on stools 

 cut across confirm the latter opinion. 



The depth of rooting is so much influenced by the condition and 

 depth of the soil that it is doubtful whether in most cases the inherent 

 character of the variety has much opportunity to show itself. 



It is possible that relative resistance is due to a difference in the 

 rate of the spread of injury from the point of puncture of the leaves by 

 the adult. Observations on this point will be made during the 

 coming year. 



NUMBERS OF FROGHOPPERS PRESENT. 



We have discussed above the relation that the various factors of the 

 environment bear to the number of froghoppers present or to the total 

 amount of " blight " or damage. 



Owing to the varying condition of the resistance of the cane it will 

 be found that the same nunrber of froghoppers do not always cause the 

 same amount of damage. Thus fields are found severely damaged by 

 an infestation of froghoppers that would in other fields have caused a 

 much less serious injury. 



The total number of froghoppers in an infested field may reach as 

 high as one hundred per stool, which is almost three hundred thousand 

 per acre. Rorer (1912) records 500-1,000 eggs per stool "by actual 

 counts," but I have never found adults or nymphs in this quantity. 



In 1906 according to Mr. -J. Arbuckle the adults were so numerous 

 that they became entangled in the horses' manes when the overseers 

 were riding i-ound the estate, and at Caroni in 1917 they got into the 

 mouths and eyes of the boys attempting to distribute sulphate of 

 ammonia through the fields. 



The largest number I have ever caught by light traps was 20,000 in 

 five lamps in one night at Harmony Hall Estate on 9th July, 1918. As 

 a general rule 20 froghoppers per stool on well grown canes means 

 visible signs of blight and with 50 to one hundred the blight will 

 be severe. 



Unless the field has been closely watched for souje time the number 

 of froghoppers seen is very misleading as the attention of the agriculturist 

 is only drawn to the fields when the damage begins to be serious and 

 in many cases this may be a week or two after the height of the brood. 



ROOT FUNGI. 



The effect of root fungus on the cane is outlined in Section VII and 

 in Section IX will be discussed the possible pai't that it plan's in the 

 final condition of the cane. It is here introduced as one of the almost 

 constant features of the blighted fields. 



Very occasionally fields, usually of plant canes, are found blighted 

 without obvious signs of one of the root fungi, but more usually they 

 are common on almost every stool and in some cases, particularly in 

 certain years, (e.g. 1918) they are so widespread as to be almost 

 sufficient to account for the production of blight withoiit any other cause. 



OTHER INSECTS. 



Carmody in 1909 (p. Ill) says that in 1908 at Oaroni the large moth 

 borer (Castnia licus) was very common, and he believed it to be partly 

 responsible for the outbreak of blight. 



