22 FROUHOPPER BLIGHT OF SUGAR-CANE. 



spots each night [for several weeks, the accumulated injurj' is very cou- 

 -siderable. A leaf often has as many as a hundred punctures and rough 

 estimates in the field frequently indicate a destruction of ten or twenty 

 per cent, of the let^f area, while in bad attacks 50 to 100 per cent, is the 

 rule rather than the exception.'-' 



The rate of spread of the injury from a puncture and the duration of 

 the different stages is subject to very considerable variation and further 

 investigation on this line might throw light on the cause of the spread. 

 The increase in size is quite oat of proportion to the original damage 

 due to the puncturing of the leaf and removal of the sap, and must be 

 due to the introduction of some poison, toxin or infection into 

 the wound. 



The first stage is noticeable about two days after the puncture by the 

 insect and spreads slowh' without any central discoloration for from five 

 to eight daj's. In rare cases as long as 15 days has been passed without 

 discoloration. A number of observations gives about seven days as the 

 average duration of the stage. 



Tlie red discoloration of the second stage begins five to fifteen days 

 .^average seven), and lasts without the death of the centre till fifteen to 

 twenty-six days (average nineteen days), after the original puncture. 



The death of the centre part of the streak defining the third stage 

 •starts on the fifteenth to twenty-sixth day and continues to spread 

 slowly until the death of the leaf a month or so later. 



On an aveiage the typical first stage is found after four da\'s, the 

 typical second stage after about two weeks, and the typical third stage 

 after three to four weeks. 



As the brood of adult froghoppers ma3" only last two or three weeks 

 it will be seen that the injury continues to increase after the adult 

 froghoppers have disappeared. 



In addition to the above symptoms the developing leaves in the 

 terminal roll receive less nourishment from the damaged plant so that 

 the new leaves are shorter and narrower than the leaves which would 

 have been produced by the same plant in normal growth. By measuring 

 the lengths of the successive leaves some time after an attack this 

 check can easily be shown. 



DAMAGE TO THE STEM. 



The damage to the stem is entirely indirect and is due to the 

 reduction of the food supply both from the injured roots and leaves, and 

 also near the tip from the spreading of injury from the young leaves 

 downwards. 



The growing jwinf of a cane badly damaged but not killed almost 

 always shows a red discoloration when cut longitudinally. In a healthy 

 cane this discoloration, probably due to oxidation, appears some 

 minutes after the surface is cut, but in the diseased canes it is already 

 there before cutting. It is most distinct at the nodes where it may take 

 the form of narrow red streaks extending up and down the vascular 

 bundles from each node, and it may spread some distance down from 

 the growing point. 



Another symptom sometimes present is the formation of small 

 pockets of a gummy substance in the young internodes. 



A caue leaf is about four feet long and two to two aiid a half inches in width, 

 tapering towards the tip. Tlie ai-ea of a healthy leaf is probably under 100 

 square inches. 



