Influence of post-harvest application rates of cyprodinil, treatment time and temperature on residue levels and efficacy in controlling green mould on 'Valencia' oranges

The effectiveness of heat treatments with water and cyprodinil in controlling post-harvest green mould caused by Penicillium digitatum was investigated on artificially inoculated 'Valencia' oranges. Residue levels of cyprodinil were determined in the oranges as a function of active ingredient concentration, temperature and treatment time. Cyprodinil residues were significantly dependent on treatment time when applied at 600 mg l-1 and 20°C, but not when fruit were treated at 150-300 mg l-1. The application of cyprodinil at 50 or 100 mg l-1 at 55°C for 30 s produced similar residue levels, while residues increased when the application rate was 150 mg l-1. Cyprodinil at 100 mg l-1 and 60°C produced a significant increase in residues compared to treatment at 50 mg l-1; no significant increase in residues was found when the application rate was raised from 100 to 150 mg l-1. In comparison to treatments performed at 20°C, the application of a heated cyprodinil mixture resulted in significantly higher residues in fruit. All treatments with cyprodinil at 20°C similarly reduced green mould after 7 days of storage at 20°C. After 18 days, treatment with cyprodinil at 600 mg l-1 for 30 s was more effective than at 150-300 mg l-1. When dip time was extended to 90 or 180 s, treatment efficacy was positively related to fungicide concentration. Treatments with water at 55°C for 30 s were as effective as cyprodinil at 50-100 mg l-1, but less effective than cyprodinil at 150 mg l-1. After 7 days, treatment with water or cyprodinil at 50-150 mg l-1 and 60°C were equally effective in controlling green mould; while, after 18 days, treatment with cyprodinil at 150 mg l-1 was consistently more effective than at 50-100 mg l-1 or hot water alone.