Efficiency of a non-recycling postharvest fungicide drencher to enhance management of apple decay and food safety

Abstract

Introduction: Recycling drenchers used to apply postharvest fungicides in pome fruit may spread microorganisms, i.e., plant and foodborne pathogens, that increase fruit loss and impact food safety.

Methods: A non-recycling field drencher (FD), which drenches unstacked bins of fruit, was compared to a commercial recycling packinghouse drencher (CPD) for fruit coverage, fungicide residues, postharvest diseases control and spread of plant pathogens, total coliforms and generic Escherichia coli. A mixture of fludioxonil (FDL) and thiabendazole (TBZ) was used in 2021, while pyrimethanil (PYR) was applied in 2022 to alternate fungicides.

Results: The overall spray coverage assessed with pyranine was not significantly different between the FD and CPD. The residue levels of FDL and TBZ were similar between the two methods on Honeycrisp apples at the top, middle, and the bottom of the bins, whereas the residue levels of PYR were significantly lower at the bottom of the bins treated through the FD. The density of plant pathogens and overall disease incidence were similar on apples drenched through both systems in 2021 and significantly lower in FD-treated apples in 2022. The incidence of blue mold, the most important postharvest disease caused by Penicillium spp., was significantly lower in apples treated through the FD in both years. The levels of total coliforms and generic E. coli were significantly higher in fungicide solutions collected from the CPD compared to the FD. Total coliforms increased significantly on apples treated via the CPD but not on apples treated through the FD.

Discussion: Findings from this study suggest that the new non-recycling drencher has potential as an alternative to recycling packinghouse drenchers in reducing the spread of plant and foodborne pathogens.

Keywords: application methods; food safety; fungicide solutions; non-recycling; postharvest diseases.

Figure 1

Illustration of the non-recycling field drencher (FD) developed and tested in this study. Dimensions are given in mm.

Figure 2

(A) Overall pyranine deposition in samples collected from bins drenched through the field drencher (FD) and the commercial packinghouse drencher (CPD). Data bars are the mean and standard errors of 32 samples per drencher type. (B) Deposition of pyranine in samples collected from the top and bottom sections of the bins drenched through the FD. (C) Deposition of pyranine in samples collected from the top and bottom sections of the bins at three different positions 1st, 2nd and 3rd high on the truck during drenching through the CPD. Data bars are the mean and standard errors of 36 values from nine samples per bin section and four bins per drencher type. An asterisk indicates significant differences based on Tukey’s test at p ≤ 0.05.

Figure 3

Overall residue levels of thiabendazole fludioxonil and pyrimethanil (A) on Honeycrisp apples and residue levels on apples collected from the top, middle, and bottom sections of bins treated through the field drencher (B) or commercial packinghouse drencher in 2021 (C) and 2022 (D), respectively. Data bars are the mean and standard deviations of 16 samples consisting of three samples of 10 fruit-each per bin section, across the four apple lots. An asterisk indicates significant difference based on Tukey’s test at p ≤ 0.05.

Figure 4

Residue levels of thiabendazole and fludioxonil (A) and pyrimethanil (B) in fungicide solutions applied through the field drencher (FD); residue levels of TBZ and FDL (C) and PYR (D) applied through the commercial packinghouse drencher (CPD) after several (0–600) bins had been drenched in 2021 and 2022, respectively. Data bars are the mean and standard deviations of 12 samples consisting of four samples per lot plated to three replicates each for the field drencher or per sampling point (number of bins) for the packinghouse drencher. An asterisk indicates significant difference based on Tukey’s test at p ≤ 0.05.