A Study of Natural Methods of Control for 

 White Grubs. 



By J. F. Illingworth. 



Disease organisms in the soil have long been recognised as useful 

 allies in the control of white grubs. Hence, I was gratified, soon after 

 my arrival in Queensland, to find that approximately one-third of the 

 grubs on the Greenhills Estate had recently succumbed to Muscardine 

 fungus. Naturally this discovery led to further investigations, especially 

 as to the cond.tions under which these friendly agents became effective. 

 Later, artificial propagation ol the disease was undertaken with some 

 success ; but this discontinued in 1920, when I found that the peculiar 

 climatic conditions had brought about an epidemic wherever spores of 

 the disease occurred naturally in grubby soils. 



The year 1920 was abnormal in many ways. First of all the rainy 

 season was very late in starting, so that it was the middle of January 

 before the first beetles emerged. The delay did not curtail their numbers, 

 however, for they came out in swarms, and, furthermore, when it became 

 time to oviposit, they were exceedingly erratic in their flight, especially 

 on the Greenhills Estate, where they extended far into fields which had 

 been regularly immune. As a result of this peculiar distribution of the 

 grubs, I have been able to work out some important facts as to the normal 

 location of disease organisms in the soil there. 



The Greenhills Estate 

 The Greenhills Estate has about 1,000 acres under cultivation. 

 Nearly half of this area — the portion with timber to the north and east — 

 has suffered for a number of years from excessive attacks of grubs. The 

 soil is of a uniform chocolate colour, of volcanic origin and great depth. 

 It is excellent ground to work, mellow as a garden, and so well drained 

 that it can be cultivated even during the rainy season. Splendid crops 

 can be grown without manures ; yet the soil is very deficient in humus, 

 a fact Avhich probably explains the tremendous d(»struction to the crops 

 from white grubs. 



