Vol 109 (1996): Proceedings of the Florida State Horticultural Society
Citrus

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

Published December 1, 1996
Keywords
  • citrus sinensis,
  • ammonium bicarbonate,
  • benomyl

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.