April, '21] ILLINGWORTH : ARSENIC FOR WHITE GRUBS 239 



We now have many experiments under way in cane areas that have 

 been regularly devastated, but it will be some time before we can hope 

 for conclusive results, i.e. as to the amount of arsenic required per acre, 

 method of application, etc. Hence I was glad to avail myself of an 

 opportunity to experiment upon troublesome grubs in the garden. 



During July and August, cucumbers which had been planted in hills 

 with cowdung, failed completely. They had hardly started to grow 

 before the leaves began to yellow, and the vines became stunted in spite 

 of the fact that they were given an abundance of water. When they 

 were dug out the soil was found to be filled with white grubs ; and there 

 was every indication that they had destroyed the small feeding roots. 

 This pest proved to be Isodon puncticollis Macleay, commonly known 

 as the Ganger Beetle, because of its destructive habit of digging holes 

 into potatoes and various root crops. 



I at once tried the application of arsenic to these hills, using the poison 

 at the rate of about 80 pounds per acre, to see if it would destroy the 

 mature grubs, leaving two hills for checks. About a fortnight later I 

 could only find two live grubs in the four treated hills, while one of the 

 checks had 46 and the other 21 full-grown grubs. 



This result was so encouraging that I prepared six new hills on Septem- 

 ber 27th, and on October ISth, when the soil was full of newly-hatched 

 grubs, I treated five of the hills with arsenic at the same rate, leaving 

 one for a check. A week later, I could find no grubs in the treated 

 hills, though two live beetles were uncovered. The check which was 

 about six feet from the others, had 61 grubs. 



An additional experiment was tried, in which the soil and dung were 

 dusted with arsenic at the time that the hills were prepared; in this case, 

 too, a single hill was kept for check. Three weeks later these hills were 

 examined; six live beetles but no grubs were found in the treated hills, 

 while numerous young grubs were in the check. 



These results are most encouraging, especially since I have been 

 able to demonstrate that the poison has no detrimental effect upon 

 growing plants, even when used in excessive quantities, i.e. 200 pounds 

 per acre. Furthermore I have found by careful chemical tests, prepared 

 by the mill chemists, that sugar cane grown on land so treated takes up 

 none of the poison — not a trace of it could be found in the juice. Growth 

 on treated soils is most vigorous, so the only possible disadvantage may 

 arise from the action of the arsenic upon soil bacteria, especially if we 

 find it necessary to use the poison in large quantities. Thi^ however, 

 can only be demonstrated after extended application. \ 



