September, 1921 



SCIENTIFIC AGRICULTURE 



Dusts and Dusting for Insect and Funjj^us Control 



In tbe, last ai-ticle entitled "The Pre- 

 sent Status of Dusting," an endeavor was 

 made to show that the process of dnstin^' 

 was an efficient and economical niethod 

 for the control of insects and fungi, under 

 the proper conditions. It is proposed to 

 supplement this by a consideration of the 

 materials which are used as dusts, and by 

 a consideration of the factors necessary 

 for successful application. This article 

 will deial with those dusts which contain 

 arsenic in some form as the insecticidal 

 principle, and copper in some form as the 

 fungicidal principle. 



Having once arrived at the conclusion 

 that the process of dusting is feasabl?. for 

 practical purposes and that it possesses 

 certain advantages over the process of 

 spray hi g, it is but natural that suitable 

 compounds of copper should receiva care- 

 ful study. It has been generally conceded 

 that, for certain plant diseases such as the 

 potato blights, copper is a much more 

 activ? fungicide than .sulphur, and under 

 epidemic conditions with most plant dis- 

 eases the superiority of copper is gener- 

 ally recognized. It is, therefore, apparent 

 that suitabl?! dust substitutes for Bor- 

 deaux spraj' should ,reeeive consideration. 



As noted in the previous article dusts 

 containing copper are not new. They 

 came into existence coincident with the 

 development of Bordeaux spray, but went 

 very little beyond the experimental stage. 

 However, prepared commercial Bordeaux 

 mixtures in dry form are made in con- 

 siderable quantity, and although these aiie 

 primarily designed for mixing with Avater 

 and for use as sprays, yet they can ob- 

 viously be utilized for dusting purposes. 

 R^ecently a copper-arsenic dust described 

 by the writers in the 1918 and 1919 •• Pro- 

 ceedings of the Nova Scotia Entomolo- 

 gical Society" has come into fairly ex- 

 tensive use. This differs fundamentally 

 from the commercial Bordeaux powders 



By G. E. SANDERS and A. KELSALL, 



Insecticide Investigators. Entomolo- 

 gical Branch, Ottawa. 



II. — Dusts Containing- Copper and Arsenic. 



and consequently 



will be considered 



separately. 



Commercial Bordeaux Dusts. 



Paris green embodying both copper and 

 arsenic in one chemical compound is the 

 best known copper-arsenic dust, but it 

 may be dismissed from practical con- 

 sideration for the following reasons : — 



1. When used in such strengths as 

 make an efficient insfecticide, the cop- 



])er content is altogether too low for the 

 requirements of a good fungicide. 



2. Its physical iwoperties, density and 

 adhesiive powers, are far from perfec- 

 tion. 



3. -If is too expensive. 



The commercial -Bordeaux po"v^^^ers are 

 of several types, for the most part made 

 by the mixture of coppei' sulphate solu- 

 tion and milk of lime, the filtration and 

 drying of the resultant precipitate, and 

 the addition of an arsenical insecticide. 

 The copper content generally varies from 

 ten to twelve per cent, but may be con- 

 siderably higher and is sometimes less. 

 The poAvder is diluted as desired Avith 

 hydrated lime or other "filler."' One 

 Avell knoAAni United States firm uses 

 magnesium hydroxide in place of lime, the 

 prec'ipitate being of course of a similar 

 character. These dusts are all of a bright 

 blue colour, are in a very fine state of 

 mechanical diA'ision, have very fair adhe- 

 sive properties, and are capable of form- 

 ing an excellent dust cloud. These char- 

 acteristics Avould lead to the supposition 

 that such dusts are excellent fungicides, 

 and experiments have shoAvn that this 

 A'icAv is correct. Experimental data is 

 shoAvn later. 



The New Copper — Arsenic Dust. 



This dust AA^as first devised in .1917, 

 but Avas merely used during that year on 

 individual plants in the greenhouse at 

 Maedonald College in order to test its 



