The Canadian Horticjlturist. 379 



DANGER OF COPPER. 



CORRESPONDENT has directed my attention to an article in your 

 October issue on the probable danger to the fertility of the soil from 

 the copper present in the solutions used as fungicides. 



I am of the opinion that Professor G. McCarthy is greatly mis- 

 taken in considering so seriously whatever element of danger there 

 may be from this source, and that, in this article, he is unnecessarily 

 sounding a note of alarm, which, though intended as a warning, may nevertheless 

 prove to be a stumbling-block to many fruit growers. 



Properly applied, i.e., at the right time and in correct proportions, the cop- 

 per fungicides have proved and are proving themselves to be of inestimable bene- 

 fit in the orchard and in the vineyard. The increased value of the fruit has more 

 than repaid, by a large margin, the outlay for spraying apparatus and materials 

 and cost of application, and I believe the time has come when no fruit grower 

 can afford to ignore this useful means of preventing fungus diseases. That the 

 least important element in successful fruit growing, now-a-days, is keeping in 

 check fungus growths and destructive insects, and, for this purpose, our present 

 hope lies in the application of arsenical and copper solutions. By the more 

 extended use of them the hope is confidently entertained that the loss occasioned 

 by injurious insects and fungi will be greatly lessened year by year throughout the 

 Dominion. I therefore crave somewhat of your valuable space, in order to place 

 before your readers my reasons for thinking that the danger to the fertility of the 

 soil, by the use of fungicides, has been unduly magnified, in the article referred to 

 in your October number. 



In the first place, the arithmetic is somewhat astray. Prof. McCarthy, if 

 correctly reported, says that six treatments of sixteen gallons each are required 

 per acre, making a total of 400 gallons, containing 108 pour^ds of copper sul- 

 phate. Should it not read 96 gallons per acre, containing about 26 pounds of 

 copper sulphate ? 



Secondly, many of the best authorities are now advocating three or four 

 sprayings instead of six, holding that the former are equally efficacious with the 

 latter, if the operation is begun early enough in the season. Granting that each 

 application requires per acre about 30 gallons, the total quantity of Bordeaux 

 mixture per acre for the season would be between 90 and 1 20 gallons, containing 

 from 24}^ to 32 jS^ pounds of copper sulphate. 



Thirdly, Bordeaux mixture has to a very large extent been replaced by cop- 

 per carbonate, either dissolved in ammonia — known as ammoniacal copper car- 

 bonate — or applied simply in suspension. When applied in suspension or 

 dissolved, the amount of copper carbonate per 25 gallons of water is two ounces 

 — a quantity containing the same amount of copper as four ounces of copper 



