54 T BIN ID AD AND TOBAGO BULLETIN. \XIX. ?. 



As the brood passes the canes are able to send out undamaged leaves 

 and gradual recovery sets in. This will vary according to the extent of 

 the original injury. The length of time taken for a plant to produce a 

 nevi^ set of leaves is however longer than the time between successive 

 froghopper broods, and as a result the cane after one attack is in a 

 weaker condition to withstand a second. This probably accounts for 

 the greater damage caused by a second brood even when its numbers do 

 not appear to be greater than the first. 



The greatest intensity of the bligirt is about two to three weeks after 

 the heiglit of the froghopper brood, but the total damage ^■a^ies greatly 

 from year to year and from place to place. 



Uncomplicated froghopper attack is distinguished from uncompli- 

 cated root disease by the presence of the brown streaks on the leaves. 

 Froghopper injury is never confined to a few isolated stools as 

 occasionally occurs in the case of root disease. Root disease further has 

 not the periodic nature of froghopper blight. The blight resembles in 

 symptoms the Sereh disease of the East, but does not become steadily 

 worse each year as with the latter. The resemblance of tlie s^ mptoms is 

 largely accidental and Sereli does not occur in Trinidad. Certain fungi 

 make discoloured spots on the leaves of the cane. The chief of these are 

 the Eye-Spot (Helniintliosporuim) and the Ring-Spot {Ltytosphaerla), 

 but the marks are quite distinct from those of froghopper injury. The 

 Eye-Spots are small, seldom more than half an inch in length, and have 

 only been found up to the present on one variety of cane, D 109. The 

 Ring-Spots are purplish-brown in colour with a paler centre and almost 

 round, seldom exceeding half an inch in diameter. In the Mosaic 

 Disease, recently discovered in Trinidad, the leaf is irregularly mottled 

 with indistinct streaks which are pale from the first and never become 

 darker than the healthy loaf. 



HISTORY OF THE BLIGHT. 



Blight, apparently similar to the present one, was recorded in 1862, 

 1869, 1878, and various years up to 1889 when the froghopper was first 

 recognised as the probable cause. From about 1890 onwards for several 

 years, the gradual degeneration of the Bourbon cane was taking place, 

 largely due to Red Rot {CoUetotrichiun). No outstanding attacks 

 appear to liave occurred again until 1906, although a few slight local 

 outbreaks are recorded in 1900. 



In 1906 commenced a series of sevete attacks which has continued 

 with occasional intervals up to the present time. The relative severitj' of 

 blight in these years is shown in a diagram, which indicates a recurrence 

 of periods of severer blight at intervals of foifr or five years. The times 

 of greatest damage were 1906-8, 1911-1912 and 1917-18. 



The weatlier conditions for each year from 1906-1919 are summarised. 



FROGHOPPERS IN OTHER COUNTRIES. 



Tobago has its own species of froghopper, Toviasph caimodyi, which 

 however has done no damage. 



In Grenada the Trinidad insect is known and in 1916 did s^evcre 

 damage in a few small areas. 



