Biological and integrated control of postharvest blue mold (Penicillium expansum) of apples by Pseudomonas syringae and cyprodinil

In an attempt to develop fungicide (thiabendazole)-resistance management strategies, experiments were carried out to determine if the control of blue mold (Penicillium expansum) in ‘Empire’ and ‘McIntosh’ apples could be achieved by a biocontrol agent, Pseudomonas syringae and enhanced by integrating a biocontrol agent and a reduced-risk fungicide, cyprodinil, in a cold storage, and in a subsequent shelf-life study. The Ps. syringae at a concentration of 1.4 × 108 CFU ml−1, or cyprodinil at a concentration of 20 μg ml−1 were effective against blue mold caused by thiabendazole (fungicide)-sensitive and -resistant P. expansum in cold storage for 30 days and in the subsequent shelf-life study at 20 °C for 6 days in Empire’ and ‘McIntosh’ apples. Cyprodinil was effective in both the co-treatment, where fungicide or biocontrol agent and pathogen inoculum were applied together, and the post-inoculation treatment, where fungicide or biocontrol agent applied 20 h after inoculation. Ps. syringae was more effective as a co-treatment than as a post-inoculation treatment. All of the eight combinations, two concentrations of the biocontrol agent (3.0 × 107 and 6.0 × 107 CFU ml−1) and four concentrations of the fungicide (5, 10, 20, and 40 μg ml−1) were more effective than either the Ps. syringae or cyprodinil alone on blue mold caused by the isolates of P. expansum collected from Ontario. Integrated control was efficient in controlling blue mold of apple and could be considered for disease control strategies to manage thiabendazole-resistant P. expansum and also for reducing fungicide residues on fruit.