277 



For the dust sprays, sulphur, lead arsenate and hydrated lime were 

 used in four different proportions, namely, 80-10-10 ; 60-10-30 ; 

 ()0-5-35 and 10-10-80. For the liquid sprays, ] lb. i)owdered lead 

 arsenate was used to 50 U.S. gals, water with the addition of 2 lb. lime. 

 For the second and third applications 4 lb. atomic sulphur, h lb. lead 

 arsenate and 2 lb. lime were used to 50 U.S. gals, water. Each 

 substance was applied with a regulation power outfit. Detailed 

 results obtained in the various test plots are tabulated. 



The results indicate that the above dust mixtures effect approxi- 

 mately 'as good control of brown rot as spraying with a combined 

 insecticide and fungicide in water and that they are far superior in 

 scab prevention. Dust mixtures are, however, less effective than 

 ^sprays in controlling C. nenuphar on varieties that ripen as late as 

 Flbertas : both spray and dust were unsatisfactory ^n this respect. 

 The comparative ineflficacy of dust against the weevil is the principal 

 weakness of the method. It is thought that a fourth application of 

 dust to Elbertas. perhaps about two weeks before maturity, might in 

 \-ears of normal abundance effect control of the pest ; future experi- 

 ments will decide this. It was found that 5 per cent, lead arsenate 

 gave as good results in control of the weevil as formulae containing 

 more lead, and with less lead there is of course less liability to injury 

 of foliage. No recommendations can be made with regard to dust 

 formulae until more work has been done on these lines. 



Tryon (H.). Root-Bark Channeller of Citrus. Decilaus citriperda, 

 H. T. (Coleoptera, Fam, Curculionidae, Sub-Fam. Cryptorrhyn- 



chldae). — Queensland Aqrie. JL. Brisbane, xiii. Februarv 1920. 

 pp. 71-82,^3 plates. [Received 20th April 1920.] 



The larva of the weevil. Denlaus citriperda, sp. n., which is described 

 in all its stages, attacks citrus roots. It was hardly noticed before 

 1917, and experiments against it were not started till the autumn of 

 1919. There are probably two generations in a year. The larvae 

 gnaw channels in the inner bark (cortex) but do not give rise to a ring- 

 barking effect, so that a strong tree will ])robablv overcome the direct 

 injury. Young traes never suffered ajjpreciably, and Seville orange 

 trees were not attacked. The trees chiefly infested were ordinary 

 oranges., lemons and mandarins. Grafted or worked trees suffered 

 more than seedling trees, but most damage took place where the trees 

 were already unhealthy. The attacks are very local, and as the adult 

 weevils cannot fly, they jjrobably ovi])osit for the most part on the 

 roots they have themselves infested. 



No reliable remedial measure has yet been discovered. Salt and 

 sulphur treatment of the soil did not produce successful results. 

 Further experiments should perhaps be on the following lines : the 

 insects might he prevented from reaching the root by some repellent 

 substance {e.g., one containing crude naphthaline) placed at the base 

 of the tree-trunk : or some gaseous insecticide may ])rove eft'ectiv^e 

 against insects already occurring in the roots : or it may be possible 

 to reach them in the burrows in dry weather with some fluid that is 

 not itself destructive to plant-tissue (e.^r.jkvanit). Strengthening the 

 roots by correct soil treatment, measures against drought, and fertili- 

 sers, prevent insect attack and also benefit the tree. 



