SECTION ir.- NATURE OF THE "BLIGHT." 25 



I have been informed that the sucrose in blighted canes inverts 

 more easily than in normal canes. 



The juice of blighted canes is further considerably more acid than 

 normal juice. This was first pointed out bv Collens (1906 A & B.). 

 iind Carmody (1909 B. p. 110) states that "wherever froghoppers are 

 imusually abundant the cane on closer examination is found to be 

 diseased from other causes and the juice is abnormally acid." He then 

 raises the question as to whether the acidity of the juice is due to the 

 sucking of the froghopper or whether the froghopper is more attracted 

 to canes which have already a juice made acid from other causes. 

 Further discussion on this question will be found on p. 126. 



Chemical change in the sap is also indicated by the spread of the 

 red brown discoloration from the point of puncture of the leaves, and 

 by its appearance in badly damaged canes on the upper part of the stem 

 particularly in the growing point at the base of the young leaves. 



FINAL CONDITION OF DAMAGED CANES. 



On Plate IV is shown a very badly damaged stool of cane with the 

 ■dead leaves removed, Plate V shows a larger stool somewhat less 

 damaged and Plate VI shows the component parts of a damaged stool 

 separated so that the effect on each shoot is more apparent. 



It will be seen that the final condition of the stool is largely 

 determined by the size and vigour af the shoots at the time of injur}', or 

 by the relative number of shoots of different sizes. The smallest shoots 

 (Plate VI, C to G) are killed outright in spite of a relatively large root 

 system ; the medium sized shoots (B) are injured but may recover ; 

 while the largest shoots (A) are much less injured and retain sufficient 

 vitality to throw out young shoots {a, a,) at the base, which will produce 

 good canes if a sufficient growing period remains and good weather 

 prevails. 



It follows that, other things being equal, the larger and more 

 vigorous the canes are in a field the less will be the probable damage. 



If however conditions continue unfavourable and the severity of one 

 or more broods is sufficiently great, the accentuation and accumulation 

 of all the above symptoms may result in the complete destruction of the 

 whole stool. All except the larj^est standing canes are killed, root 

 fungus spreads with great rapidity on the already damaged stools, the new 

 shoots fail to establish themselves and the plant, unable to stand the 

 ■drain on its reserves, becomes a complete loss to the grower. • 



The ground between such stools soon ceases to be shaded and grass 

 and weeds grow rapidly and assist in smothering and starving the cane 

 plants, which are finally covered up by a growth of weeds and creepers. 



RECOVERS. 



If conditions become favourable and the original damage has not 

 been too severe, a rapid recovery sets in after the passing of the flight of 

 adult froghoppers. 



The younger leaves as they unfold are no longer punctured and 

 •damaged, but remain healthy and green, and the stool and field gradually 

 assume a healthier appearance as the proportion of green leaves 

 increases. 



At the edge of a damaged field recovery in this way is noticeable by 

 the high level of the distinct line made by the brown leaves. The 

 lower leaves are dead, the middle leaves are damaged only at the tips 

 which hang down, and the youngest ones are green. 



