Influence of formulation and application method on the effectiveness of benzimidazole fungicides for controlling postharvest diseases of citrus fruits

Abstract

Treatment of citrus fruits after harvest with benzimidazole fungicides suspended in water or incorporated in wax formulations can control the development of several diseases of the fruit during storage and marketing. Residues of 1 mg fungicide/kg fruit are sufficient to retard the development of latent infections of Phomopsis and Diplodia and to prevent wound infection by Penicillium spp. Sporulation of Penicillium spp. on the surface of decayed fruit, a serious problem in long distance shipment of citrus fruits, can be controlled by minimum residues of 2–6 mg fungicide/kg fruit, depending upon the composition of the residues on the fruit. On an equivalent residue basis, benomyl is considerably more effective than thiabendazole or methyl benzimidazol-2-ylcarbamate (MBC) in reducing sporulation of Penicillium on treated fruit. Benomyl appears to penetrate into the flavedo tissue of the orange whereas residues of MBC and thiabendazole are limited to the surface of the fruit. The effectiveness of the benzimidazole fungicides is not influenced by the variety or size of citrus fruits but is significantly affected by the formulation and method of application. MBC and thiabendazole are stable under most conditions of formulation and application but benomyl breaks down in alkaline wax formulations and in organic solvent formulations. Deposits of thiabendazole on fruit resulting from application of a water-wax formulation are less effective in controlling sporulation than an equivalent deposit applied as a suspension in water.