Some observations on size and biological activity of spray deposits produced by various formulations of copper oxychloride

Chemical estimations and biological assays, using Botrytis fabae, of spray deposits on beans (Vicia faba) in the laboratory have shown that the amount of an initial spray deposit of copper oxychloride is dependent on the volume of application used per unit area and the concentration of copper in the spray liquid. The addition of 0.1 % of an anionic surfactant (dioctyl sodium sulpho-succinate) greatly reduced the amount of these initial deposits although another anionic surfactant did not. In the laboratory trials the fungitoxicity of the spray deposit was related to the actual copper levels initially present. In general, the addition of surfactants improved the fungitoxicity of the initial deposit. The addition of surface-active agents did not materially affect the rain-resistance of the spray deposits, while their presence in emulsions of PVA, PVC and PVB gave an improved biological performance. All three polymeric materials greatly improved the tenacity of copper oxychloride spray deposits without reducing their fungitoxicity in laboratory tests. When examined in field experiments against potato blight (Phytophthora infestans) these apparent biological advantages due to the tenacity and good distribution of the polymeric emulsion formulations did not materialize. An explanation for this apparent contradiction between laboratory and field data has been given based on certain features of the epidemiology of the pathogen.