STUDIES UPON THE COPPER FUNGICIDES

Abstract

SUMMARY.1. To overcome difficulties encountered in the application of Bordeaux mixture as a fine mist‐like spray, two modifications are proposed which may be applied in larger quantities after the manner of an insecticidal wash. By this means the application of the protective fungicide is made easier and more rapid, the wear on the spray pumps may be reduced and difficulties due to the lack of carrying power of the spray are removed. Further, the incorporation of a contact insecticide with the protective fungicide becomes possible, with resultant saving of labour and of time in the routine spraying of fruit and hops.2. The modifications of Bordeaux mixture proposed are (1) the incorporation of concentrated sulphite lye in the Bordeaux mixture, (2) the glyceride oil emulsion produced by the use of Bordeaux mixture as emulsifier. As examination of the amounts of copper retained on foliage after spraying showed that the presence of oil improves the retention of spray deposit, the content of copper sulphate and lime of the oil‐Bordeaux emulsion was reduced to half that of the Bordeaux mixture used in comparisons of fungicidal efficiency by field trials.3. The results of field trials show that, under the conditions prevailing in 1931 and 1932, (i) the modified Bordeaux mixtures, applied in heavy amounts, proved as effective as lighter applications of Bordeaux mixture for the control of potato blight, apple and pear scab. In one trial, in which vegetable oil of high free‐fatty acid content was used, the fungicidal efficiency of the oil‐Bordeaux emulsion was below that of Bordeaux mixture containing double the amount of copper sulphate and lime; (ii) the application of large quantities of the modified Bordeaux mixtures did not cause greater leaf injury or fruit russeting than Bordeaux mixture used in smaller amounts; (iii) combinations of nicotine with the modified Bordeaux mixtures gave washes of insecticidal efficiency equal to that of nicotine‐soap wash; (iv) as a result of the use of a spray of larger volume, the application of the modified Bordeaux mixtures was easier and more rapid than that of Bordeaux mixture.4. A method is described for the estimation of copper retained on sprayed foliage.