Sensitivity of Podosphaera xanthii to registered fungicides at-risk for resistance related to their efficacy for powdery mildew in pumpkin

A seedling fungicide sensitivity bioassay was conducted on 24 Jul 2007 at the start of powdery mildew development on Long Island, NY, in research plantings of squash and pumpkin (Cucurbita pepo) not treated with powdery mildew fungicides. Based on these results, the proportion of the pathogen popula...

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Bibliographic Details
Published in:Phytopathology 2008-06, Vol.98 (6), p.S102-S102
Main Authors: Mcgrath, M T, Miazzi, M M
Format: Article
Language:English
Subjects:
Cucurbita pepo
Podosphaera xanthii
Online Access:Get full text
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Summary:A seedling fungicide sensitivity bioassay was conducted on 24 Jul 2007 at the start of powdery mildew development on Long Island, NY, in research plantings of squash and pumpkin (Cucurbita pepo) not treated with powdery mildew fungicides. Based on these results, the proportion of the pathogen population estimated to be resistant to QoI (FRAC Group 11) fungicides was 82%; 72% and 44% were tolerant of myclobutanil (Group 3) at 20 and 120 ppm, respectively; and 26% and 2% were tolerant of 125 and 175 ppm boscalid (Group 7). No powdery mildew developed on seedlings treated with 5 to 20 ppm quinoxyfen (Group 13). Fungicides with these active ingredients were evaluated on pumpkin in an adjacent experiment with applications applied weekly starting at the action threshold (31 Jul to 5 Sep). Quintec (quinoxyfen) was most effective, providing 81% control on lower leaf surfaces based on AUDPC values. Control was 78% with Procure (triflumizole, Group 3), 60% with Endura (boscalid), and 58% with Pristine (boscalid + pyraclostrobin). Based on a seedling bioassay conducted in this experiment on 10 Aug, 13% of the pathogen population tolerated 5 ppm quinoxyfen, 23% tolerated 175 ppm boscalid, and 11% tolerated 120 ppm myclobutanil. On 2 Oct, 9% tolerated 10 ppm quinoxyfen, 22% tolerated 200 ppm boscalid, 11% tolerated 120 ppm myclobutanil, and 2% tolerated 120 ppm triflumizole.
ISSN:0031-949X