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POSTERS: Chemical control

The influences of infection timing and postharvest fungicide applications on perennation of the downy mildew pathogen in hop
Briana Claassen - Oregon State University. David Gent- US Department of Agriculture, Agricultural Research Service

Downy mildew of hop, caused by the biotrophic pathogen Pseudoperonospora humuli, overwinters in buds and crowns of hop plants as systemic mycelia within the plant. The impact of infection timing on pathogen survival and subsequent disease development in the next year is not well understood. To describe this process, batches of hop plants were inoculated monthly from June to October and the following year emerging shoots were rated for downy mildew. In 2017, plants inoculated in October had significantly less disease than plants inoculated in earlier months. In separate experiments, plots in commercial hop yards and experimental plots were treated with fungicides up to 4 times weekly following harvest. Experimental plots treated with fungicides had a slight decrease in downy mildew infection in the following year as compared to nontreated plots. Taken together, the early findings of this research indicate that infection leading to overwintering can occur over a broad period of time, but overwintering of the pathogen is reduced when infection is delayed until after September. Experiments are being repeated in 2018 and 2019 to validate these findings and refine management strategies for the disease.