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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #431690
Research Project: Knowledge Based Tools for Exotic and Emerging Diseases of Small Fruit and Nursery Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: Fungicide sensitivity profiles of Botrytis isolates from blueberry and red raspberry fields in Washington and Oregon

Author
item BARAL, ROSHANI - University Of Nebraska-Lincoln
item Delong, Jeffery
item STEELE, MARY - Washington State University Extension Service
item Stockwell, Virginia
item MATTUPALLI, CHAKRADHAR - Washington State University Extension Service

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2026
Publication Date: 3/26/2026
Citation: Baral, R., DeLong, J.A., Steele, M.E., Stockwell, V.O., Mattupalli, C. 2026. Fungicide sensitivity profiles of Botrytis isolates from blueberry and red raspberry fields in Washington and Oregon. Plant Disease. https://doi.org/10.1094/PDIS-01-26-0162-RE.
DOI: https://doi.org/10.1094/PDIS-01-26-0162-RE

Interpretive Summary: The $490 million blueberry and red raspberry industry is threatened by the fungal disease gray mold (fuzzy berries), caused by Botrytis species. Growers spend tens of millions each year in fungicide applications, trying to manage the disease. However, it is not known if these fungicides are effective due to the emergence of fungicide resistance. A survey of 1013 isolates of Botrytis found that 80% of the isolates are tolerant to one of the four FRAC groups tested (FRAC, 7, 9, 11, 17) and 12% of the isolates had tolerance to all four of the FRAC groups tested. These data indicate that growers must carefully choose which fungicides they will apply based on the resistance patterns in their fields and those of their neighbors in order to effectively manage gray mold. It also indicates that our ability to manage gray mold is diminishing.

Technical Abstract: Botrytis spp. cause major economic losses for small fruit growers in Washington and Oregon, the top blueberry and red raspberry-producing states in the United States. Pre-harvest and post-harvest fruit rots are conventionally managed through repeated within-season applications of fungicides from various Fungicide Resistance Action Committee (FRAC) groups. As such, monitoring fungicide resistance profiles of Botrytis spp. from small fruit fields is crucial. To this end, in 2022 and 2023 a total of 708 and 305 Botrytis spp. isolates were obtained from blueberry (WA and OR) and red raspberry (WA) fields, respectively. These isolates were screened against technical grade fungicides at discriminatory doses using in vitro conidial germ tube growth assays. Across years, isolates from blueberry showed varying resistance frequencies to fungicides tested: pyraclostrobin (68%; FRAC 11), azoxystrobin (62%; FRAC 11), boscalid (60%; FRAC 7), fluopyram (49%; FRAC 7), fluxapyroxad (38%; FRAC 7), fenhexamid (34%; FRAC 17), isofetamid (21%; FRAC 7), pyrimethanil (19%; FRAC 9), and cyprodinil (4%; FRAC 9). Botrytis isolates from red raspberry displayed the highest resistance frequency to fluopyram (79%), followed by pyrimethanil (31%), boscalid (30%), fluxapyroxad (22%), isofetamid (21%), and cyprodinil (6%). Cross-resistance was prevalent for fungicides in FRAC group 11 and for various fungicide combinations within FRAC group 7. The unique fungicide resistance patterns seen here compared to previous studies in the Pacific Northwest and elsewhere highlight the need for ongoing fungicide resistance monitoring in small fruits.