On the Value of Poison Bait for Controlling Cane Grubs. 



Siiiniiiarising results sliown by tlie foregoing figures, it was found 

 that ten out of seventeen grubs placed with poisoned leaves were dead 

 and partially discoloured a day after treatment, and by the end of fifteen 

 days 100 per cent, had j^erished, controls remaining perfectly normal. 



The alfove result was, of course, highly satisfactory as far as it 

 went, but it was necessary to detcn-mine how long these leaves would 

 continue palatable and the insecticide effective when subjected to damp 

 conditions underground. Foliage that had been poisoned for this pur- 

 pose and theii buried 6 inches deej) between rows of cane was accordingly 

 dug up after the lapse of a fortnight, and discovered to b.' more or less 

 rotten, the leaves having quite lost their rigidity. Fungi were present, 

 but the soil in contact with the surface of the leaves was not matted 

 with mycelium to a serious extent, as frequently happens with other 

 vegetable baits of a more or less starchy nature. 



On the 8th of iMarch fragments of these decaying leaves were placed 

 in six cages with second stage grubs of Lepidiofa alboliirta (table oiiiitted 

 here for sake of brevity), and when examined fouiteen days later all 

 were dead. Thus it was proved that cow-pea foliage poisoned with 

 copper arsenate will remain palatalile and deadly in the ground for at 

 least twenty-seven days. 



The question of application was the next step, and I concluded that 

 the simplest way. requiring least handling, would be to sow the peas 

 in a single line about 1 foot from the stools on each side of a row of 

 cane, and when the resultant plants were a few inches high, (hist and 

 ])lough them under in such manner as to bury th(^ poisoned leaves against 

 the main roots of the cane, where grubs when moving about in the soil 

 would be most likely to meet with them. The adoption of this method, 

 however, Avould necessarily entail an appreciable loss of material, it being 

 impossible to treat the foliage without at the same time dusting the 

 surface of the ground to some extent. For several reasons it seemed 

 wisest to adopt the above-mentioned simple method of application, and at 

 the same time reduce expenditure to a minimum by diluting the chemical. 



In the following table it will be seen that Paris green mixed with 

 three times its weight of stale tiour proved fatal to about 58 per cent, 

 of cane grubs in one week, 75 per cent, in fifteen days, and 100 per cent, 

 after the lapse of twenty-five days. 



