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Project Leaders:
Meg McGrath, Dept. of Plant Pathology, Riverhead
Carol MacNeil, Vegetable Specialist, CCE Ontario, Wayne, Yates and
Steuben Counties
John P. Gibbons, CCE,Vegetable Extension Program in Ontario, Wayne,
Yates and Steuben Counties, and NEWA, NYS IPM Program
Alan Erb, Vegetable Specialist, Lake Plains Vegetable Program
Cooperators:
Ted Blomgren, Vegetable Specialist, Capital District Vegetable Program
Chuck Bornt, Vegetable Specialist, Capital District Vegetable Program
Abby Seaman, Area Vegetable IPM Specialist, WNY
John Mishanec, Area Vegetable IPM Specialist, ENY
Rick and Laura Pedersen, Pedersen Farms, Stanley
Curt Petzoldt and Jim Engel, Vegetable Systems Project, NYS IPM Program,
Geneva
Additional cucurbit growers in other participating county
Type of grant: Monitoring, forecasting, and economic thresholds
Project locations: Ontario County, Suffolk County and Lake Plains Counties
Abstract:
Systemic fungicides are an important tool for managing powdery mildew,
the most common disease of cucurbit crops throughout the world. Unfortunately,
most systemic fungicides are at risk for resistance development because
they have single-site mode of action. Thus modification of one gene
in the pathogen may be enough to enable the pathogen to resist the action
of the fungicide. The cucurbit powdery mildew fungus has demonstrated
a high potential for developing resistance. First detections of resistance
to QoI (strobilurin) fungicides in North America occurred in 2002 and
included New York. Although resistance has developed, QoI fungicides
will continue to be valuable for managing powdery mildew and resistance
to DMI fungicide until resistant pathogen strains become common. To
use QoIs wisely, growers need to know the proportion of the pathogen
population that is QoI resistant before the first application and how
much the population changes with QoI use. Through this project, QoI
resistant strains were found to be uncommon at the start of disease
development. However, where they occurred (Suffolk County), their frequency
increased dramatically after QoI and DMI fungicides were used. QoI resistant
strains were common in most pumpkin fields examined in September, including
1 of 2 organic production fields examined and a field where neither
QoI nor DMI fungicides were used. This information, along with recommendations
on how to modify fungicide programs, was provided to growers during
the growing season through newsletter articles. Thus growers were able
to avoid unnecessary applications of an expensive fungicide during the
second half of the epidemic when QoI resistant strains were sufficently
common that QoI fungicides were unlikely to have been effective. Monitoring
needs to be continued in the future to determine where QoI resistant
strains are sufficiently uncommon that this group of fungicides will
be effective. When resistance first developed to DMI fungicides, for
several years these resistant strains were uncommon when powdery mildew
started to develop, thus these fungicides continued to provide some
control.
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