Postinfection Activity, Residue Levels, and Persistence of Azoxystrobin, Fludioxonil, and Pyrimethanil Applied Alone or in Combination with Heat and Imazalil for Green Mold Control on Inoculated Oranges

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Abstract
The postinfection activity of azoxystrobin (AZX), fludioxonil (FLU), and pyrimethanil (PYR), applied alone or in combination with imazalil (IMZ), in controlling postharvest green mold in ‘Salustiana’ oranges inoculated with Penicillium digitatum was studied. Fruits were immersed for 30 or 60 s in (i) water or water mixtures at 20 °C containing AZX, FLU, or PYR at 600 mg/L; and (ii) IMZ at 600 mg/L, alone or in combination with AZX, FLU, or PYR at 600 mg/L. Similar treatments were performed at 50 °C using the active ingredients at half rates with respect to the treatments at 20 °C. Fungicide residues in fruits were analyzed following treatments and after 14 days of simulated shelf life at 17 °C. AZX or FLU mixtures at 20 °C for 30−60 s similarly but moderately reduced green mold decay with respect to control fruit; differences due to dip time were not significant. Superior control of decay was achieved by PYR and, especially, IMZ, applied alone or in combination with AZX, FLU, or PYR. The activity of PYR at 20 °C was significantly dependent on treatment time, whereas that of IMZ and combined treatments at 20 °C was not. The effectiveness of FLU or PYR mixtures at 50 °C in controlling decay was similar and superior to that of AZX. The action of single- or double-fungicide application was not dependent on dip time in most samples. IMZ or combined mixtures at 50 °C were consistently more effective with respect to single-fungicide treatments with AZX, FLU, or PYR. The application of heated fungicide mixtures resulted in significantly higher residue accumulation in most fruit samples compared to treatments performed at 20 °C. The degradation rate of fungicides was generally low and dependent on treatment conditions such as time, temperature, and the presence or not of other fungicides.

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