EVALUATION OF FUNGICIDES FOR MANAGEMENT OF DEFOLIATION CAUSED BY MYCOSPHAERELLA CITRI (GREASY SPOT) IN 'HAMLIN' ORANGE

MCGOVERN, R. J.

Abstract


Our objective was to compare the effectiveness of an experimental bicarbonate-based fungicide alone and in combination with benomyl, with two standard emulsified oil formulations in managing defoliation by Mycosphaerella citri Whiteside (greasy spot) in orange [Citrus sinensis (L.) Osbeck]. The experimental site was in a commercial grove of 6- year-old 'Hamlin' orange trees in southwest Florida. Fungicide treatments, a novel formulation of ammonium bicarbonate [(AB) 0.5% w/v], benomyl (2.2 kg a.i./ha), a reduced-rate combination of bicarbonate and benomyl (0.25% w/v + 1.1 kg a.i./ha), and petroleum distillates FC-435-66 (70 l/ha) or FC-455-88 (70 / l ha), were applied on 6 Jul., 1994 by a commercial air-blast sprayer calibrated to deliver 1400 l/ha. Each treatment and an untreated control was replicated 6 times using ten-tree blocks arranged in a randomized complete block design. Percentages of tree defoliation were estimated on 15 Nov., 20 Dec., 1994 and 27 Jan. and 24 Feb., 1995 using the Horsfall-Barratt disease rating scale. All treatments reduced the rate of greasy spot defoliation and all but benomyl reduced the final percentage of defoliation. FC 455-88 and AB plus benomyl were generally the most effective and the other treatments were of intermediate effectiveness in reducing greasy spot defoliation.

Keywords


citrus sinensis; ammonium bicarbonate; benomyl

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283