MONTHLY NOTES ON GEUBS AND OTHER CANE PESTS. 5 



Apparently the general custom in all the grub districts has been 

 to destroy the principal humus-forming elements by burning all the 

 trash and failing to rotate cane with a green crop. So far we have only 

 discovered one farmer who is working his land along the lines that 

 science would suggest, and it is interesting to note that his farm, though 

 originally rather poor land, is now among the best in the region about 

 Gordonvale. Furthermore, he is not troubled with grubs, though the 

 cane on near-by farms went down because of them. Moreover, this 

 particular farm has better soil to-day than when it was opened up 

 about twenty years ago. As to the treatment: the land was given a 

 dressing of lime at the rate of about 1 ton per acre. A crop of beans 

 was then turned under, preparatory to planting cane. After two ratoons 

 and ploughing in all the trash another croj) of beans was worked into the 

 soil, and in addition about 5 cwt. of meatworks manure per acre. This 

 rotation has been followed up, with the result that our tests now show 

 an abundant supply of humus. Recently with the addition of about 

 2 cwt. of nitrate of soda per acre this land has shown remarkable 

 results. The crop is easily 50 per cent, better than that of the adjoining 

 farm, which was planted at the same time. I must not neglect to add that 

 this farmer cultivates well, which is not only an important factor in 

 plant development, but may be shown to have considerable bearing 

 upon grul) control. This control would come about through the con- 

 servation of soil moisture, which would not onl^^ stimulate the growth 

 of the cane, making it more resistant to the attacks of grubs, but the 

 conserved moisture would also be of material assistance to the develop- 

 ment of fungous organisms destructive to the grubs. These parasites 

 cannot work in dry soil, hence it is a well-recognised fact that grubs are 

 most destructive in a dry season or upon dry soils. 



The action of nitrate of soda or sulphate of ammonia is a marked 

 stimulation of j^lant-growth and root-development, which makes the 

 -cane more resistant to the attack of grubs. Where there is a rapid renew- 

 ing of roots as they are eaten off by grul)s, the cane is able to hold its 

 footing, and does not go down before the winds. This point was well 

 illustrated in one field that we visited, a part of which had been treated 

 with about 2 cwt. of sulphate of ammonia per acre. The cane of part 

 of the field was all down, Avhile right to the line in the treated plot it 

 stood erect and vigorous. The untreated portion could not be ratooned, 

 because all the stools were too much out of the ground. 



As far as our observations have gone, the indications are that high- 

 lying fields are attacked worse than those on low-lying ground. This 

 may be explained upon the ground of w^eathering. Naturally, both 

 humus and lime are leached out of high-lying soils, and tests show these 

 soils to be very poor in both these elements. 



The use of arsenious poisons for the destruction of the grubs, as 

 suggested by Mr. Jarvis, is very promising. Since we already know 



