Field trials with Bordeaux mixture and various formulations of copper oxychloride for control of late blight of potatoes and black pod of cacao

Abstract

Results of field trials for the control of potato blight ( Phytophthora infestans ) in the United Kingdom, and of black pod disease of cacao ( Phytophthora palmivora ) in West Africa, have yielded information on the mode of action of Bordeaux mixture. The experiments were designed to compare the disease-controlling properties of Bordeaux mixture with those of a copper oxychloride wettable powder (WP) and of a copper oxychloride suspension supplemented by colloidal aluminium hydroxide. The latter adjuvant was chosen as a result of earlier laboratory studies. The following conclusions are drawn from the data, (1) Bordeaux mixture does not always give better disease control than a copper oxychloride WP suspension of equal copper content. (2) Copper oxychloride suspensions supplemented by the appropriate concentrations of aluminium hydroxide gave results almost identical with those of Bordeaux mixture both against P. infestans and P. palmivora . (3) The superiority of Bordeaux mixture and the supplemented oxychloride over oxychloride WP is attributed primarily to the physical characters of these spray liquids; more particularly to the fact that both Bordeaux and the aluminium hydroxide supplement are irreversible, deformable hydrogels. (4) The particle size of all copper oxychloride samples used in these experiments was considerably greater than that of the active ingredient of Bordeaux mixture. It has been shown in the field, however, that the reduced toxicity often associated with greater particle size can be offset by a suitable alteration in the physical characteristics of the fungicide suspension.