116 FROGHOPPER BLJOHT OF SUGAR-CANE. 



Occasionally a field of canes is badly damaged as plants and yet gives 

 an excellent crop of ratoons. This merely indicates that conditions in 

 the field have in some way changed and does not in any way effect the 

 truth of the statement that, other things being equal, the younger canes 

 are less liable to damage than the older. 



In the above the word "plant-canes" means the well grown canes 

 eight months or more from the date of planting, but occasionally the 

 3'oung, just sprouting canes are damaged late in the year. Several 

 examples of this could be given, and they seem usually to be 

 caused by planting the young cuttings in a field from which the old 

 stools have not been removed and the froghoppers are able to carry over 

 •without being destroyed as would occur under a proper system of rotation. 



Reference has already been made to one unusual case in which adult 

 froghoppers were found throughout the whole dry season of 1918 in a 

 field of young plant canes. 



Among the ratoon canes there is a difference in age of the shoots 

 above ground according to whether the field is cut early or late in crop 

 time. On a field cut at the beginning of crop in February the ratoon 

 shoots have three or four months longer to grow than in a field cut at 

 the end of crop. Growth is of course slow at this period of the year, but 

 considei-able gain in yield is made by the earlier cut fields. Accurate 

 data on the subject are much needed. 



It might be expected that the ratoons that were earliest cut and that 

 had longest growth would be less damaged by froghoppers owing to their 

 larger size. However, the only two cases in which uncomplicated 

 evidence on this question is available seem to indicate the reverse. 



At Harmony Hall Estate in 1919 there were two contiguous 

 fields of Uba cane, all second ratoons and all previously similarly 

 treated, with the soil very uniform throughout. 



A corner of one field was accidentally burnt and cut on 1st April 

 (1). The rest of this field was cut in the middle of May (2). The field 

 alongside was cut in the middle of June (3). 



The first brood of froghoppers appeared at the beginning of July, 

 was large and did distinct damage on 1, was medium and did slight 

 damage on 2 and was very small and did no visible damage on 3. The 

 largest growth was most damaged and the smallest growth least so. 



The first plot may have been affected by the burning, but between 

 the other two there was no known difference in previous treatment 

 except the date of cutting. 



Another case was seen at Orange Grove m 1919 when two fields of 

 second ratoons, mixed varieties, in similar soil were side by side. The 

 canes cut at the end of February and beginning of March were larger but 

 much more severely blighted than those in the field cut at the beginning 

 of May. Another field of the same canes alongside, but cut towards 

 the end of May was still smaller and almost free from damage, but in 

 this case the field was first ratoons, although otherwise similar. 



These two are the only cases in which all other factors can be 

 eliminated and if significant it would appear that the covering up of the 

 ground by canes throughout the greater part of the dry season produces 

 conditions not favourable to the froghopper, or perhaps more favourable 

 iiO the survival of its egg parasites, (see p 103). 



