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Reduction in the number of fungicide applications for lettuce downy mildew by timing application based on aerial spore load
Nikhilesh Dhar: UC Davis; Amy Anchieta: USDA ARS; Frank Martin: USDA ARS; Steven Koike: Univ of California; Krishna Subbarao: University of California at Davis, c/o U.S. Agricultural Research Station; Steve Klosterman: USDA ARS
<div>The downy mildew pathogen, <i>Bremia lactucae,</i> is an obligate, host-specific oomycete pathogen that infects lettuce. Characteristic symptoms include chlorosis of the infected leaf tissue followed by the appearance of sporulation on the abaxial side of the leaves. Mildew symptoms decrease market value of the produce and the sporulation results in secondary spread. Due to the heterogeneity and quick adaptation of this pathogen in the field, calendar-based fungicide applications have been the most effective means to manage downy mildew. However, repeated applications of chemicals has led to fungicide resistance in the pathogen. The previously developed qPCR assay specific to <i>B. lactucae </i>coupled with a solar-powered spore trap system for detection of <i>B. lactucae</i> was deployed in the current work to measure <i>B. lactucae</i> spore load at three commercial fields that each contained experimental plots. Based on the inoculum thresholds detected, fungicides applications were scheduled. Following spray advisories conserved approximately 1.7 sprays on average, relative to the calendar-based sprays. Deployment of this approach in commercial field can reduce grower costs and fungicide use in lettuce production while also decreasing the development of fungicide resistance in <i>B. lactucae</i>.</div>

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