10 On the Value of Poison Bait for Controlling Cane Urubs. 



In spite of tliis failure in diluted form the ehiinis of arsenious acid 

 as a suitable insecticide for tighting the cane-grub deserve recognition, 

 owing to its being fully six times as cliea]) as Paris green ; for we have 

 already seen that both these arsenicals when nndilutt^d occasion abont 

 the same percentage of mortality. 



The quicker action of Paris green may ])rove to be an uniinpurtant 

 factor in the present instance, since grubs atfected by either poison })rob- 

 ably cease feeding, and provided that all ultimately perish it matters 

 little whether some die sooner than others. 



Owing to the greater solubility (*f arsenious acid and its i)urning 

 action on foliage, it is seldom recommended as an orchard spray uidess 

 in combination with lime or various chemicals; but, again, such draw- 

 backs do not necessarily apply to its application underground in a dry 

 form, although ])ossibly during wet weather foliage dusted in this way 

 may rot more quickly than would be the case were it treated with copper 

 arsenate. If deemed advisable the soluble arsenates in commercial white 

 arsenic could be easily rendered insoluble. 



There is no necessity, however, to discuss the sul)ject more fully 

 just now, but I may mention than in achlition to its triMing cost this well- 

 knt)wn arsenical is considered to be less jjoisonous to man than Paris 

 green, and, as a rule, is freer from adulteration with foreign substances. 



MODE OF PREPARING AND ADMINISTERING THE BAIT. 



The most favourable time to start the ])reparatory work of drilling 

 in cow-peas for bait would be about three \veeks after the first general 

 appearance of Gray-back Beetles, as we should Wwn disturb the soil 

 shortly after oviposition and probably break up numy egg chambers, hi 

 the event of an occurrence of protracted dry weather it might l)e found 

 advisable to sow a little sooner in order to talce advantage of moisture 

 still remaining from the heavy rain that usually ushers in the first 

 emergence of these beetles. 



Having got the peas to germinate and come up, their after growl h. 

 if retarded, would not matter much, our object ))eing to ol)tain stock'v 

 plants, bearing, say, a dozen leaves, and together making a comi)act line 

 of foliage about 6 inclies high liy 8 inches broad. Should the rows exceed 

 these dimensions, a month after sowing they could be dusted and 

 ploughed under in the maimer already desei'ilied on page 7. but it' 

 dry weather should liap])en to keep the plants stunted it would be better 

 to allow six weeks from date of sowing 1o elapse l)efoi'e ti-eatment. as cane 

 gi'ubs would by thai time have moulted to the second stage, in which 

 they manifest a greater liking for xcgeTablc food and acquire increased 

 powers of locomotion. 



To ensui'e couii)lete burial in the nutst laxourable |)osition. it might 

 be found necessai-y to ])lough a trench close alongside the stc)ols, sow the 

 peas in the bottom, and later on. after dusting the plants, turn a fui-row 

 on top of tluMU, tile weight of which would tend to press the i)oisone(| 

 leaves downward to the requisite depth. 



