SUPPLEMENTS FOR COPPER FUNGICIDES 95 



analogous to the dissociation of electrolytes whereby the poisonous prop- 

 erties are altered. From the above one concludes that the copper in 

 fungicides must not only be soluble but ionized to become active, and 

 that the activity is proportional to the concentration of the copper ions 

 and the potential availability to the total ionizable copper, although the 

 copper in undissociated compounds may undergo decomposition and be- 

 come appreciably active. Soluble copper in itself is not a true criterion 

 of activity. 



A considerable range in activity may be obtained with different fungi- 

 cides, such as basic, slightly alkaline, neutral, and acid Bordeaux mixtures, 

 Burgundy, the acetates, cuprammoniums and copper sulfate, and with 

 different concentrations; but toxicity to foliage, poor adhesiveness, invis- 

 ibility and difficulty of preparation practically preclude the use of some 

 of these products. Supplements, however, have been employed by various 

 workers and the process generally consists of adding to Bordeaux or 

 Burgundy mixtures substances known to produce soluble copper in alka- 

 line mixtures. These substances may be divided into three groups (a) 

 sugars, etc. (b) hydroxy-organic acids and (c) biuret compounds. The 

 resulting soluble compound is usually electronegative and the solution 

 purple or violet. 



(a) Of the first group may be mentioned sucrose, dextrose, lactose, 

 dextrin and glycerol. They produce soluble copper, but mixtures with 

 dextrose, lactose and dextrin are particularly liable to decompose on 

 standing, with the precipitation of cuprous oxide which is not rated highly 

 as a fungicide. 



In numerous tests with Bordeaux 4-2-50 in the station laboratory, solu- 

 ble copper was observed with 0.016 per cent sucrose, 0.080 per cent lac- 

 tose, 0.160 per cent dextrin and 0.801 per cent glycerol, but probably 

 occurred in lower concentrations. In most instances the Bordeaux was 

 made with drj', laboratory-prepared hydrated lime after being soaked over 

 night. The amount of added substance varied generally from 0.008 to 

 0.160 per cent of the spray although larger amounts were employed oc- 

 casionally. 



Many investigators have used sugar and molasses with Bordeaux, Bur- 

 gundy and special mixtures in field practice. Pons (77), Perret (71, 72) 

 and Barth (cited 5, p. 295, 296) claim that such preparations are more 

 active, non-toxic to foliage and of good suspension and adhesive properties. 

 Doran (22, p. 541) found that sugar and molasses increased the toxicity 

 of Bordeaux to conidia of apple scab fungus. The reaction between 

 Bordeaux and sugar, excluding the calcium hj'droxide, is said to be sub- 

 stantially as follows: 



CiiHnoOn+HsO =2 CoHiiOe 



2C6Hi206+302=2(CHOH) 4(COOH),+2H,0. 



2(CHOH)4(COOH)2+2CuS04 5H20=2(CHOH)4(COO)2 Cu-f2II,S04 



+ 10H,O. 



According to the above equation, 1 part of sugar converts 1.46 

 parts of copper sulfate into 1.59 parts of copper saccharate and renders 

 soluble 0.37 parts of copper. Investigators recommend generally 5 per 

 cent as much sugar or 10 per cent as much molasses as of copper sulfate 

 which, if applied to Bordeaux 2-2-50 and 4-4-50, would yield approximately 

 0.01 per cent and 0.02 per cent soluble copper. 



(b) Pickering (75, p. 174, 184, 190) and others have shown that hydroxy- 



