Septeml-er, 1921 



SCIEXTIFIC AGRICULTURE 



able limits. Coiist-Miuently the original 

 i'onmilae used were later moilified. Of 

 i-ourse it is also- desirable to use differing 

 formulae for different plant diseases and 

 different insects, and for usie on different 

 plants, in the same way as various modi- 

 fications of ordinary Bordeaux mixture 

 are now recommended. 



The composition of the dust has always 

 been expressed by the writers in terms of 

 the per cent of metallic copper and the 

 per cent of metallic arsenic. The dusts 

 used vn the apple in the large field experi- 

 ments in 1919 contained three per cent of 

 metallic copper and one per cent of metal- 

 lic arsenic, while those used on the large 

 fields of potatoes, contained five per cent 

 of metallic copper and two per cent of 

 metallic arsenic. These diists were ex- 

 pressed as 3-1 dust, and 5-2 dust, res- 

 pectively, and this sj'Stem of nomencla- 

 ture is well understood and in frequent 

 use bv farmers and fruit growers in the 

 Annapolis Valley. Since 1919 a 31/0-I14 

 dust has been used on apples and 5i/2-'-^ 

 used on potatoes. 



For purposes of calculation it may be 

 stated that the dehydrated copper sul- 

 phate generally contains 35 per cent 01 

 metallic copper, and that calcium arse- 

 nate generally contains 26 per cent of 

 metallic arsenic. Thus Si/o-lVi dust is 

 composed of ten pounds of dehydrated 

 copper sulphate, five pounds of Calcium 

 arsenate, and eighty-five pounds of hy- 

 drated lime. 



For mixing, an ordinary dust mixer is 

 used, one similar to those in use by the 

 larger bakeries for mixing flour. This 

 is driven by a small gasoline engine. For 

 the writers' experiments a dust mixer 

 owned by Mr. S. B. Chute, of Berwick, 

 has been used. This has a capacity of 

 a hmidred pounds, and wnth it two men 

 can mix three, tons of dust per day, 

 making the cost of mixing about twenty- 

 five cents per hundred pounds. The 

 mixed dust is fairly bulky and a package 

 of about four thousand five hundred cubic 

 inches should be allowed for each one 

 hundred pounds of dust. In Nova Scotia 

 in 1921 on the basis of purchases already 

 made, the mixed dust is being delivered 

 to the grower for $6.00 per hundred 

 pounds. 



Properties of the Dust. 



After mixing, the dust may be .stored 

 in any ordinary dry place. It should, 

 however, be used during the same si8asx)n 

 in whicli it is mixed. Otherwise there is 

 some tendency for the material to collect 

 in lumps and prove unsatisfactory. 



Containing, with the exception of water, 

 all the ingredients which form an ordinary 

 poisoned Bordeaux, it is only natural that 

 on contact Avith Avater on the leaf surface, 

 the dust should form a blue Bordeaux mix- 

 ture. If the dust is applied to a dry foli- 

 age then the first dew or moisture which 

 subsiequently occurs on the leaves, changes 

 the dry Avhite dust to a film of poisoned 

 Bordeaux. All using the dust have been 

 particularly struck by the spreading 

 poAver in comparison Avith sulphur dust. 

 In the experimental orchard, fifty-five 

 pounds Avere sufficient to thoroughly dust 

 an acre, Avhile seventy-three pounds of 

 90-10 sulphur-lead arsenate dust were re- 

 quired for the same area. The sprayed area 

 required one hundred and fifty' gallons 

 per acre. 



It AA-as realized at the commencement of 

 these dusJt investigations that the relative 

 poAA-ers of adhesion to foliage of the dust 

 and thl? spray, Avere important factors in 

 their relative fungicidal and insectidical 

 value. In addition it Avas realized that 

 from an economic standpoint it was im- 

 portant to knoAv the relative amounts 

 adhering to the foliage, in proportion to 

 the amounts actually projected on to the 

 plant or tree. It AA^as assumed at first 

 that in the application of dust a propor- 

 tionately larger amount of the material 

 fell to the ground, or Avas bloAvn aAvay, 

 than in the application of spray. There 

 AA-ere no definite grounds for this assump- 

 tion, and indeed it seems to have been 

 founded on thi? fact that dust floating 

 through the air attracts more attention 

 than spray falling to the ground. To 

 determine these questions expleriments 

 AA'ere made Avith foliage from the large 

 orchard plots. 



Adhesion Experiments. 



At various intervals through the sum- 

 mer of 1919 five hundred or a thousand 

 leaves were picked from trees • from the 

 dusted area, and the same number picked 



