Biocontrol agents have not met with significant commercial success for post-harvest applications and have remained relegated to small niches despite the market need for methods to reduce the development of resistance to chemical products. Biocontrol agents have the following disadvantages:
1. Special handling and timing and use restrictions. Some biocontrol agents cannot be tank mixed with other fungicide products because the fungicides will kill (and thus deactivate) the biocontrol agent. This limits their use and negates the most positive reason to use them: resistance management. Also, when a biocontrol agent is an antagonist to the pathogen, timing the application is crucial. The microorganism must be applied shortly before or at the same time as exposure to the pathogen for efficacy. This reduces the agent's practicality in packinghouses.
2. Efficacy. Efficacy reports are mixed largely because users expect to use a biocontrol product like a chemical without special regard to timing and handling. Efficacy can equal or approach chemicals if the biocontrol agent is used exactly as required and directed, with an understanding and appreciation of the mechanism of action.
3. Shelf stability. Some biocontrol agents do not produce spores and consist only of bacterial cells or fungal mycelia, and as a result the shelf life of a biocontrol product may not match that of a chemical product. Maintaining a high degree of viability and efficacy in formulated biocontrol agents can be a challenging task. As with most pesticides, biofungicides are commonly dehydrated into powder or concentrated into liquid formulations. Such processes can have a negative impact on disease control efficacy. As most information on the formulation of biopesticides is proprietary, there is limited literature on the subject. For example, freeze-drying of Candida sake caused cell mortality and greatly affected control of blue mold of apple, compared to that obtained with fresh cells . Protective agents and additives, such as skimmed milk, peptone, or lactose, at the time of freeze-drying and rehydration can somewhat help reduce cell mortality of C. sake . As mentioned above, growing yeast cells at low osmotic potential can be used for better desiccation adaptation .
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