12 On the Value of Poison Bait for Controlling Cane Grubs. 



CONCLUSIONS. 



it must be l)orne in iiiiiid that i-esults now recorded relate exelusively 

 to cage experiments, and have yet to be confirmed in the field. Apart 

 from .such considerations, however, the present Bulletin, which announces 

 a cheap, simple, and presumably effective means of combating' tlie grub 

 stage of our most serious cane insect, cainiot fail to be of interest to all 

 concerned in the sugar industry. 



At the risk of being thought too oi)tindstic. I do not hesitate to say 

 that future field investigations in this connection are not likely to reveal 

 the presence of any vital obstacle to final success. 



The clnef points requiring settlement l)y such field work will relate 

 primarily to the question of rainfall, and its effect on the solubility and 

 efficiency of both forms of arsenical; and to various operations of a 

 mechanical nature which will enable us to determine the simplest and 

 most economical method of dusting and burying the poisoned cow-peas. 



It need scarcely be stated that the plan of jirocedure outlined in this 

 Bulletin relates solely to treatment of the late crop, which at Gordonvale 

 is planted from August to October, and is the one principally attacked. 



It is my intention to combat the larva a.s far as i)ossible during its 

 second stage, at a time when young plant and ratoon cane would not 

 be high enough to interfere Avitli the field work connected with this 

 control method. 



With reference to the behaviour of the grub under natural con- 

 ditions, it is well known that although leading a subterranean life it 

 constantly changes its position, becoming especially active during wet 

 weather ; hence we may reasonably assume that while travelling among 

 the main roots, feeding, and ingesting soil, it can hardly fail to encounter 

 the bait before able to work appreciable damage. 



Rich volcanic soils of a deep and friable nature att'ord ideal con- 

 ditions for the development of cane grubs, and it is worth noting that 

 this class of land — seen at Greenhills, Meringa, and other districts — is 

 precisely the one most likely to benefit from the application of poison 

 bait, owing to the fact that grubs are able to move nbout in it with 

 facility. 



Field ex])eriments cannot be expected to yield pei-centages of 

 nioitality as higli as those shown on the accom|)anying tables, for the 

 .sim[)le reason tliat grubs confined in small cages of soil must ])erforce 

 soon discover the bait, whereas, under natural contlitions, owing to the 

 \-ery ei-ratic movements of the pest and the i)resence of other vegetable 

 food, a larva migiit on occasion feed for days close to poisoned leafage 

 without perceiving it, or even miss it altogeth(;r. I'lKiuest ionahly, tins 

 would seldom ha{)pen if the treated leaves were ailificiaily renderetl 

 enticing enough to induce grul)s located within a ratlins of from -4 to 

 ti inches to mo\'e towards them. 



