AbstractThe mildew fungicide triforine is incompatible with calcium chloride used to reduce the incidence of bitter pit in apples. Two commercial non‐ionic surfactants delayed sedimentation in spray mixtures containing both triforine and calcium chloride. The biological efficiency of triforine, alone or with calcium chloride plus surfactant, was tested in an orchard trial which included binapacryl, alone or with calcium chloride, as ‘standard’ treatment. Triforine (weekly or fortnightly) controlled mildew on Cox's Orange Pippin and Golden Delicious better than binapacryl, and the addition of calcium chloride did not affect adversely the control by either fungicide. The added calcium chloride had little effect on the deposition and persistence of the fungicides. The inclusion of calcium chloride in spray programmes slightly improved the yields (both cultivars) and russet grade (Cox only) associated with each fungicide. Calcium chloride sprays, whether mixed or alternated, increased the calcium levels in postharvest fruit for both varieties, and decreased the incidence of bitter pit for Cox after storage for 5½ months. No adverse effect was associated with the inclusion of the surfactants in tank mixtures containing either fun
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