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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research » Research » Publications at this Location » Publication #337058

Research Project: Improved Strategies for Management of Soilborne Diseases of Horticultural Crops

Location: Horticultural Crops Research

Title: Screening Phytophthora rubi for fungicide resistance

item Weiland, Jerry

Submitted to: Washington Small Fruit Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/6/2017
Publication Date: 1/10/2017
Citation: Weiland, G.E. 2017. Screening Phytophthora rubi for fungicide resistance. Washington Small Fruit Conference. Whatcom Ag Monthly. 5(12).

Interpretive Summary: Phytophthora root rot is a serious disease that can cause 100% crop loss. We collected, identified, and tested Phytophthora species from red raspberry fields for resistance to a commonly used fungicide, mefenoxam. Most of the Phytophthora isolates that we collected were identified as Phytophthora rubi, though individuals from one field were tentatively identified as a different species, Phytophthora megasperma. All individuals, regardless of species, were sensitive to the fungicide mefenoxam. This is important because many growers use fungicides to manage Phytophthora root rot. If fungicide resistance was present, it would be more difficult for growers to manage this disease.

Technical Abstract: Preliminary results from the survey for fungicide resistance in Phytophthora were reported at the 2016 Washington Small Fruit Conference. Phytophthora was isolated from diseased plants in 28 red raspberry fields and tested against mefenoxam, the active ingredient of Ridomil. Most isolates were identified as P. rubi, but isolates from one field were a different species tentatively identified as P. megasperma. Most isolates were sensitive to mefenoxam, however P. rubi was slightly more sensitive to the fungicide than P. megasperma. Tests for sensitivity to phosphorous acid and other fungicides are underway.