26 



FROGHOPPER BLIGHT OF SUGAR-CANE. 



If the damage has originally proceeded to a stage when most of the 

 younger shoots have been killed and only the older ones remain with 

 normal growing points, the latter will recover as described above, but 

 the field will be characterised by the number of small dead shoots round 

 the base of the stool. (Plate IV.) 



If the damage has been still more serious, so that the larger canes 

 have had their growing points injured, the recovery will be very uneven 

 and mostly by the shooting of the upper eyes in these canes, and by 

 fresh healtbj' shoots breaking out from the old root stock and basal 

 joints of the canes. 



With the continuance of good conditions a remarkable'recovery may 

 take place, even in cases of severe damage, but the canes never make 

 up what they have lost and the appearance of such a field is deceptive, 

 as the new growth of leaves frequently serves to cover up a coiuplete 

 absence of cane development beneath. 



The rate of return to normal growth depends on the original damage 

 and on the ability of the cane to produce new leaves and shoots. 



No special investigation has yet been made of the rate of root 

 production, but in the absence of root disease this is probably rapid, 

 and proceeds as usual in step with the development of leaf surface. 



A number of observations have been made on the rate of production 

 of new leaves and these show that a cane plant produces a new leaf every 

 four to seven days according to conditions and the time of the year, 

 and as a healthy plant should have 10 to 15 green leaves, it follows 

 that two to three months are required for a plant to throw off all the 

 damaged leaves and replace them by healthy ones. 



In Fig. 4 an attempt has been made to measure the rate of recovery 

 by estimating the percentage of efficiency {i.e. green assimilating tissue) 



Fig. 4. 



pi„_ 4— Diagrams of eflSciency of green leaves of dainagtd ami unilamaged canes 

 For explanation see text. 



