74 PROTECTION OF PLANTS — 1922-23 



Nicotine Combinations. 



If we pour free nicotine into a copper sulphate solution we get a blue nico- 

 tine Bordeaux. Just what the status of copper nicotine sulphate is as a contact 

 insecticide, I am not prepared to say, but I do know that such a compound is 

 highly undesirable in a nicotine dust where the volatile nicotine only is of value. 



The presence of dehydrated copper sulphate in a nicotine dust cuts down 

 the volatility of the nicotine by about one-third. In the same wa> the presence 

 of acid lead arsenate reduces the volatility of the nicotine. The presence of 

 organic matter or the presence of moisture also retards the volatility of nico- 

 tine. The making of nicotine dusts is a very particular operation and for the 

 greatest economy and efficiency only straight nicotine dusts should be used. 

 "Three in One" and "All in One" dusts mixtures are inefficient, costly and 

 undesirable. 



Copper Arsenic Dusts. 



Three types of copper dusts, in addition to the dried Bordeaux powder that 

 has been offered for so many years, are now being offered. 



Blue Copper Arsenic Dust. 



This dust is made up of monohydrated copper sulphate, hydrated lime and 

 arsenate of lime. It is called Blue dust on account of it turning blue when 

 brought in contact with water. It is when applied merely a mechanical mixture 

 of the three ingredients, combination taking place or Bordeaux salts being form- 

 ed when the material comes in contact with moisture on the plant leaves. While 

 this material is light and fluffy the active ingredients in it will onJ|r pass a 200 

 — mesh screen. 



The high limits of a 200-mesh, monohydrated copper sulphate in this type 

 of dust are 35 per cent on the potato and 20 per cent on the apple. By using 

 magnesium hydrated lime and getting the copper sulphate ground extra fine 

 a higher percentage of copper sulphate be used with safety. In practice I do not 

 find it advisable to go beyond 25 per cent of monohydrated copper sulphate 

 for the potato and 15 per cent of monohydrated copper sulphate for the apple 

 in this type of dust. 



Lead arsenate has been used b}^ us in this type of dust and is insisted upon 

 by some experimenters. Lead arsenate increases the cost and does not seem to 

 me any more desirable as cDmpared with arsenate of lime than it is in liquid 

 Bordeaux. 



Superfine dust collector white arsenic was used by me in this type in my 

 own orchard one season with no injury. Mr. Kelsall used it in his orchard with 



