Alternatives for the use of DPA: Critical minimum DCA storage exposure periods followed by RA and CA storage to inhibit superficial scald on Packham’s Triumph pears

Previously, the South African apple and pear industry relied on diphenylamine (DPA) for controlling superficial scald disorder; however, increasing consumer concerns and reductions in maximum residue levels (MRLs) highlighted the urgent need for alternative control strategies. The aim of the project is to optimise an effective alternative technique to the use of DPA by determining the critical minimum storage period that fruit needs to be exposed to DCA storage conditions to inhibit superficial scald, and the effects of RA storage following DCA storage on the development of superficial scald.

Initial low oxygen stress (ILOS) in combination with CA, DCA and RA for 2 ,3, 5 and 7 months including a simulated shipment RA period with shelf-life was tested in 2012 and 2013 seasons. Additional trials were conducted in 2014-2016. Optimum harvested ‘Packham’s Triumph’ pears from the Ceres and Grabouw production areas were used. Fruit were stored at DCA conditions for 5 d, 2 w, 4 w, 8 w, 12 w, 16 w and 20 w, then subjected to additional RA periods for 6 w and 10 w and shelf-life periods for 0 and 7 d at 20°C to determine the critical minimum exposure period to control superficial scald effectively. The efficacy of intermittent DCA periods, with exposure periods of 10 d, 4 w, 8 w, 16 w and 32 w to control superficial scald, was determined (2014-2016 seasons). Quality evaluations were conducted on fruit of each treatment at each storage period combination according to industry standards. The main focus was on the development of superficial scald during evaluations.

DCA-CF successfully inhibited the development of superficial scald on Packham’s Triumph from Grabouw and Ceres production areas for up to 20 w storage followed by 6 w and 10 w simulated shipment with 7 day shelf-life. ILOS+CA controlled superficial scald for 16 w followed by 6 w and 10 w simulated shipment with 7 day shelf-life for both production areas. It is possible to apply an intermittent DCA period of 32 w (with a 14 day RA break) with 6wk shipment with shelf-life without superficial scald development. No off-tastes were detected at any of the treatments.

DCA-CF can be recommended as a non-chemical alternative for medium to long term storage of ‘Packham’s Triumph’ pears with a 10 w shipment period to prevent superficial scald. DCA is already implemented by the South African pear industry. ILOS+CA is effective for short term storage of Packham’s Triumph. The efficacy of DCA is not reduced by intermittent breaks of 14 days RA between DCA periods of up to 32 w.