Abstract

Black spot (caused by Guignardia citricarpa) is a major disease affecting the citrus industry in subtropical Queensland. A number of chemicals were tested for control of black spot, including the strobilurins (azoxystrobin, trifloxystrobin, pyraclostrobin and methoxycrylate); a plant activator (acibenzolar); copper-based fungicides (copper ammonium acetate, copper oxychloride, copper hydroxide plus ferric chloride, cuprous oxide); mancozeb; phosphorous acid; captan and iprodione. In all experiments, the strobilurins used alone, or incorporated with copper and mancozeb, were as effective, or better than, the industry standard of copper and mancozeb. Acibenzolar used alone significantly reduced the severity and incidence of black spot by up to 50% compared with the untreated control, but was not as effective as the industry standard fungicides. No significant differences in disease control were found between the four different copper types. Phosphorous acid and captan were ineffective, but iprodione was as effective as the industry standard fungicides. The strobilurins induced less rind damage than the industry standard products, and pyraclostrobin was less toxic to the predatory mite Amblyseius victoriensis than the industry standard products.