24 FROGHOPPER BLIGHT OF SUGAR-CANE. 



Shooting of the Ei/en. When the growing point of the cane is injured 

 in any way, or ceases to require nourishment, as after arrowing, the 

 eyes or buds lower down usually start to grow. This is a frequent 

 accompaniment of the froghopper blight. Shooting usuallj^ starts just 

 below the level of the maximum shortening of the internodes and may 

 spread through thfse to those above. This breaking of the buds only 

 occurs in canes which have sufficient reserve strength to supply the 

 necessary- nutriment and so is usually seen only in the lai'ger canes of 

 the stool as in plate IV. 



Adventitious Roots. Tj sually as a direct result of the damage to the 

 root system and of the humidity produced about the stem by the 

 matting of the leaf sheaths, the dormant roots on the lower parts of the 

 cane start into growth underneath the sheaths in the attempt to get 

 more moisture. At first this occurs oialy near the base of the plant biit 

 as these roots in turn become diseased, it proceeds higher and higher up 

 the plant until developing roots may in extreme cases be found three 

 feet or more above the base. This sjauptom, as with the breaking of 

 the ej'es, usually only occurs in the larger canes with more reserve food 

 material and although frequently associated with froghopper attack, 

 may be produced by many other causes. 



DAMAGE TO THE ROOTS AND ROOT STOCK. 



The root system of a severely blighted cane is almost always, but not 

 invariably, poor and superficial. Further experiments are needed on the 

 exact effect of the sucking of the nymph on the roots, but results obtained 

 so far indicate that this alone does not produce such severe ettects as 

 are caused by the adult on the leaves. The problem is complicated by 

 the fact that blighted canes are most commonly seen in heavy poor 

 soils, which are themselves conducive to a poor root system; and 

 further that both the unfavourable soil condition and the damage by 

 the nymphs seem to assist the development of root fungi which invade 

 the diseased roots and continue the destruction. 



In addition to the weak superficial nature of the roots they are 

 frequently.blackened and dead throughout and even rotting and decayed 

 and the whole stool can usually' be pulled from the ground without 

 gi'eat effort. 



On the other hand blighted canes are found in some cases with 

 apparently sound deep root systems. Th^^se are invariably in good 

 well cultivated soils and such canes always recover with great rapidity 

 after the passing of the brood of froghoppers. 



Tlie ifoot stock, or that part of the cane below the ground is some- 

 times discoloured by a red staining such as is found in cases of rraot- 

 disease, but as at present no cane has been found in this condition 

 without root fungi also being present, it is probable that it is due to 

 these and not to the uncomplicated attack by froghoppers. 



EFFECT ON SAP OF CANE. 



The greater part of the sugar in the juice of the cane is manufac- 

 tured in the leaves of the plant. Severe injury to these leaves will 

 therefore be expected to have its effect on the composition of the sap. 



Fm'ther investigation is needed in this direction, but at present a few 

 observations have been made which should be summarised here. 



The adult is known to suck the sap from the plant and extract the 

 sugar from it. All this is direct loss to the i'lanter. Gough (1911 C. 

 p. 11) points out that the blighted canes when they come to the factory 

 contain less moisture and hence often a higher percentage of sucrose 

 than undamaged canes, but on the other hand the greater dryness of 

 the cane renders extraction less effective. 



