Senior Plant Pathologist
Technical Assistant, Outspan Citrus Centre, P.O. Box 28, Nelspruit 1200 South Africa
University of Pretoria, Department of Microbiology and Plant Pathology, Pretoria 0002 South Africa
Four copper sprays and copper mixtures with dithiocarbamates aggravated stippling of the fruit rind of Valencia oranges if sprayed in succession at registered rates during the recommended protection period from October to January for control of citrus black spot in South Africa. Copper stippling was more severe on treatments in which copper oxychloride was sprayed in succession, individually, or in combination with mancozeb or maneb/ZnO. On the other hand, less copper stippling was observed on treatments in which three mancozeb applications were altered with a single copper oxychloride as tank mixtures with or without mancozeb, which was sprayed during midsummer (December and January). Cupric hydroxide resulted in more general copper stippling lesions than any other copper oxychloride spray program. Four successive applications of the wettable powder copper oxychloride formulation resulted in more copper stippling when compared with the suspension concentrate formulation. Stippling was calculated to be more severe with late applications of copper fungicides during December and January. In another experiment, all contact fungicides tested were effective in controlling citrus black spot.