Studies on the ageing of copper fungicides used to control coffee leaf rust

Field assessments of copper fungicides used to control coffee leaf rust have indicated an effective life of a few weeks, whereas residues can be determined chemically on the leaves for several months. The studies reported in this paper were designed to study this discrepancy. The amounts of copper which were dissolved by three aqueous solvents from deposits of a cuprous oxide formulation, a copper oxychloride and Bordeaux mixture were determined at various intervals after spraying; as also were the amounts of copper physically removed. The levels of rust infection in the field following single spray applications, which had undergone various periods of natural weathering before the infection period, were recorded. No evidence of chemical deterioration was derived from the aqueous solvent studies but the data on physical weathering indicated that the initial loss of deposit was rapid and suggested that natural weathering could result in the fungicide deposit becoming insufficient to give disease control. Some evidence on the form of the loss of copper from the different fungicide deposits was obtained.