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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 #430779
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: Differential responses of Botrytis isolates to Pristine, Luna Tranquility, Switch, and their active ingredients

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

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2026
Publication Date: 3/25/2026
Citation: Baral, R., Steele, M.E., DeLong, J.A., Stockwell, V.O., Mattupalli, C. 2026. Differential responses of Botrytis isolates to Pristine, Luna Tranquility, Switch, and their active ingredients. Plant Disease. https://doi.org/10.1094/PDIS-12-25-2509-SC.
DOI: https://doi.org/10.1094/PDIS-12-25-2509-SC

Interpretive Summary: The $490 million in Washington and Oregon Blueberry and raspberry industry suffers significant economic losses due to Gray mold caused by Botrytis cinerea. Gray mold management relies on applications of various site-specific fungicides from bloom through harvest. Botrytis is notorious for developing fungicide resistance; so many commercial fungicides are pre-mixes of two fungicides to slow the development of resistance. Botrytis isolates collected from grower fields were found to have increased tolerance to individual fungicides in the premixes Pristine and Luna Tranquility. However, apple pathogenicity assays indicated that the commercial premixes Luna Tranquility and Switch were still effective against tolerant Botrytis isolates. This works demonstrates that applications of premix fungicides with different modes of action remains an essential strategy for sustainable gray mold management for small fruits in the PNW.

Technical Abstract: Botrytis cinerea is an adaptable, high-risk pathogen capable of developing resistance to several site-specific fungicides. To manage gray mold, blueberry growers in Washington state and Oregon follow spray regimes that include rotation of site-specific fungicides, tank-mixing site-specific fungicides with a multisite fungicide such as captan, and using premix fungicides to slow down selection of B. cinerea populations with resistance to site-specific fungicides. In this study, we conducted conidial germination assays to assess responses of B. cinerea isolates to discriminatory doses of three premix fungicides (Pristine, Switch, and Luna Tranquility) and their active ingredients (boscalid and pyraclostrobin, cyprodinil and fludioxonil, pyrimethanil and fluopyram, respectively). Of the 676 B. cinerea isolates tested, 430, 493, and 369 isolates showed in vitro resistance to boscalid, pyraclostrobin, and Pristine, respectively. Interestingly, 6% of the 657 B. cinerea isolates tested showed in vitro resistance to Luna Tranquility but 329 (50%) and 131 (20%) isolates exhibited resistance to the individual active ingredients fluopyram and pyrimethanil, respectively. None of 345 B. cinerea isolates germinated on sucrose agar amended with 1 µg/ml of Switch. Apple fruit inoculation assays supported responses of B. cinerea isolates to fungicides obtained from conidial germination assays on agar media. In addition to confirming the in vitro efficacy of Luna Tranquility and Switch, we discuss an array of responses exhibited by B. cinerea isolates when exposed to premix fungicides or their individual active ingredients.