Sustainable Brown Rot Management of Peaches in the Southeastern United States
Abstract:There are ways to reduce disease pressure in commercial orchards, including the removal of fruit mummies from the tree canopy, pruning out cankers and removal of wild plums surrounding orchards. However, these measures do not prevent brown rot disease, and growers are still dependent on the application of fungicides for blossom blight and pre- and postharvest disease management. Many fungicides are available for brown rot control, but few are effective enough to meet the demands for high quality fruit production. Currently, the most efficacious fungicides belong to the benzimidazoles (MBCs), demethylation inhibitors (DMIs), anilinopyrimidines, quinone outside inhibitors (QoIs), and the succinate dehydrogenase inhibitors (SDHIs). Although the anilinopyrimidines have been successfully used to control brown rot in some areas, including California, they underperform in the moist and warm climate of the southeastern United States, further decreasing the arsenal of chemical weapons for southeastern growers. These highly effective chemical classes are considered reduced-risk fungicides due to their low application rates and low toxicity towards applicators, consumers, and the environment. The low toxicity is partially a consequence of their single-site modes of action, which in turn is also the basis for major concern. For the pathogen to become resistant, a single mutation in its DNA may often suffice. Such mutations occur typically in the gene encoding the target enzyme of the fungicide. Over-expression of the target gene may also cause high levels of resistance capable of overcoming field applications of commercial products. Fungicide resistance can develop within a few years of market introduction (as was the case for MBCs and QoIs), leading to complete resistance in the pathogen population (qualitative resistance). In contrast, resistance can also build up slowly over time (quantitative resistance), as was the case with the DMI fungicides. Resistance in the brown rot pathogen has been reported for the MBCs, DMIs, QoIs and SDHIs, raising concerns about the sustainability of brown rot disease management. To date, resistance in the southeastern USA has occurred in localised pockets, largely due to fungicide preferences in specific areas, and populations with resistance to multiple fungicides have not yet emerged. The need for location-specific resistance profiling prompted the search for a simple and reliable assay to be used by county agents. Involving county agents in this project increases awareness among agents and growers in regard to the fungicide resistance problem and provides a new tool to conduct science-based consulting. This paper outlines the development, testing and verification of this location-specific resistance monitoring system.
Document Type: Research Article
Publication date: October 1, 2010
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