12 AUSTEALTAX SUGAB-CANE BEETLES AND THEIR ALLIES. 



the same drought-stricken appearance described above. Under such- 

 conditions no cane develops, hence the final result is nuich the same : 

 the crop is a total loss. 



With early planting (i.e. ]\Iarch-April) of grubby fields, unless 

 they have l)een thoroughly worked for several months, the numerous full- 

 grown grubs which are normally in the soil at that season at once attack 

 the sets, which either do not grow at all, or if they do start the shoots 

 are pale and attenuated, so that they often die out altogether. Examina- 

 tion then shows that not only have the roots been mostly eaten off, but 

 both the sets and the shoots also are often considerably gnawed into 

 (Plate 2), especially at the cut ends of the former, the grubs themselves 

 being often located in the cavities they have made. Under such condi- 

 tions it is practically useless to replant the field until these grubs have 

 hibernated. 



^Moreover, the young plant cane is frequently injured by grubs at 

 other seasons than that noted in the last paragraph, especially the late 

 planted crop, in certain areas. This, however, is the work of grubs of 

 other species, notably those requiring two years for the life-cycle. In 

 forest areas about Gordouvale the large third-stage grubs of Lepidiota 

 frencM, which come up out of their deep hibernating chambers about 

 September, are capal)le of doing as severe damage, especially to young 

 cane, as the grubs of the greybacks do at other seasons. In the scrub 

 areas here this species is replaced by two others, L. vaudata and 

 L. froggatti, both of Avhich may do as much damage. 



In the Cairns district the grubs of L. frcnclii have proved a serious 

 pest, since the third-stage grubs last for a full year in the soil, and are 

 destructive to cane-roots for several months before the season for the 

 greybacks l)egins. The general result of their work on the plant is the 

 same ; Init the appearance of the field is usually quite diff'erent, for they 

 work more in patches ; there will be here and there an area a chain or so 

 across where the cane is almost dead, while the surrounding cane i,s 

 thrifty and green. 



As I have indicated above, the change in appearance of grubby cane 

 may be very sudden, especially following a considerable rainy period, if 

 the weather turns dry ; for then the few roots still remaining, whicli 

 sufficed to supply the needs of the plant while evaporation was slight, 

 suddenly prove quite inadequate, as indicated by a piping of the leaves 

 even before they begin to yellow. This rolling of the leaves while there 

 is still sufficient moisture in the soil is thus the earliest sign that the 

 plants are suffering from root injury and lack sufficient moisture. Hence 

 the general impression that the grubs are worse in dry weather is 

 undoubtedly incorrect, for investigation demonstrates that most of the 

 damage was done before, even during the rainy season, at which time the 

 grubs work principally near the surface. This leads me to speak of the 

 value of deep-rooting varieties of cane. 



On several occasions I have called attention to the grub resistance 

 of D 1135, which is undoubtedly due both to its habit of deep rooting' 

 and its superior vigour. The roots are numerous and extend to a depth 

 of 16 to 20 inches — far below the normal activities of the grub. Then, 

 too, with this variety new roots are developed rapidly, hence the stool 

 maintains its grip on the soil even in the face of severe hardship, and 

 does not uproot. It is most instructive to see stools of this variety green 

 and upright, in the midst of a field of Badila that has entirely succumbed 

 to the attack of grubs. 



