Develop a storage protocol for plums stored for 6 weeks in bins prior to packing – decay control using alternative gas regimes of CO2 and O2 manipulation, fungicides and GRAS products by drenching and ozone treatment

Decay control is an ongoing problem in the stone fruit industry. There are still too few postharvest treatments available for stone fruit. Numerous technologies are available in other industries [i.e. controlled atmosphere (CA) storage, drenching/dipping, UV, ozone]. The aim of this study is to test different technologies to reduce decay of plum.

Different inoculation methods (spray and pipette inoculation) and spore concentrations of Botrytis cinerea and Monilinia laxa were evaluated on Angeleno plum. Three CA storage regimes (6% O₂:15% CO₂, 9% O₂:12% CO₂ and 12% O₂:9% CO₂) and regular atmosphere (RA) were tested. Six dip treatments (Bestcure 1X and 2X, HyperCide 1X and 2X, fludioxonil, fludioxonil and pyrimethanil) and untreated control (UTC) were tested. Two O₃ gas treatments (1h application time, 2h application time) and UTC were tested. Integrated methods were tested that included O₃ (2h application), CA (6% O₂:15% CO₂), O₃ & CA, and RA storage with (Bestcure and fludioxonil) or without (UTC) fungicide treatments. Plums were stored for ±6w at -0.5 °C and 10d at 10 °C (shelf life) before evaluation.

CA regime 1 (6% O₂:15% CO₂) and 2 (9% O₂:12% CO₂) significantly reduced decay; decay severity reduced by 65% with regime 1 and 50% with regime 2. CA regime 3 was ineffective. Bestcure was ineffective and HyperCide showed low levels of control (depending on method and concentration). Since fludioxonil provided 100% control, the contributing effect of pyrimethanil was not noticeable. The 2h application of O₃ (>0.14 ppm) was the most effective O₃ treatment. With regards to treatment integration, plums treated with combinations of O₃ & CA, O₃ and fludioxonil exhibited the lowest disease incidence, decay severity and sporulation compared to CA, RA and in most cases Bestcure. O₃ on its own and in combination with CA were the most effective gas treatments and fludioxonil the most effective fungicide treatment. The treatments and treatment combinations did not have a negative effect on the quality and taste of Angeleno plums.

Combining O₃, CA storage and fungicides resulted in improved efficacy against B. cinerea and M. laxa on Angeleno plums. The treatment combinations thus show potential to reduce decay, extend storage life and can be used to assist in reducing fungicide resistance build-up, and maintain or gain access to stringent markets by lowering MRLs (depending on implementation and management). More research is needed to include other stone fruit types and cultivars, and continue optimisation of an integrated control method.