The Crush - April 2019 - 1

Volume 46 Issue 4 April 2019


Powdery Mildew: Managing Fungicide Resistance
By Ted Rieger
Grape powdery mildew (PM), caused by the fungal pathogen
Erysiphe necator, is the most common grapevine fungal disease
in California. More chemicals are used annually for managing
PM than for any other grapevine pest or disease.
The use of sulfur as a fungicide is an integral part of many
PM management programs, and it has never shown resistance
problems. However, the use of sulfur can have limitations based
on weather conditions, and it may require longer restricted entry
intervals into the vineyard after applications. Other fungicide
chemistries provide growers alternatives to sulfur use and can
provide benefits in extending application intervals.
PM fungicide resistance to certain foliar fungicides has been
known to occur for nearly 50 years. In the 1980s, the international
Fungicide Resistance Action Committee (FRAC) was established
to classify fungicides by their chemical modes of action and
help growers understand how to identify products and alternate
fungicide chemistry applications for resistance management. PM
resistance has been identified and is being studied in four classes
of fungicides used on grapes:
1. Sterol demethylation inhibitor (DMI) fungicides, FRAC 3.
Product examples: Rally, Procure.
2. Quinone outside inhibitor (QoI) fungicides, also called
strobilurins, FRAC 11. Product examples: Flint, Abound.
3. Succinate dehydrogenase inhibitor (SDHI) fungicides, FRAC 7.
Product examples: Endura, Luna Experience.
4. Azanaphthalene (AZN) fungicides, FRAC 13. Product
example: Quintec.
Dr. Walt Mahaffee, research plant pathologist
with USDA's Agricultural Research Service
(ARS) in Corvallis, Ore., and his team
have been developing tools to assess PM

Powdery mildew is the most common fungal disease of grapevines in California.
Photo: Fred Rehrman

fungicide resistance in western U.S. vineyards to chemistries
within the FRAC 11 and FRAC 3 categories. Research funding
has come from the American Vineyard Foundation and research
organizations in Oregon and Washington.
In 2018, Washington State University (WSU) viticulture extension
specialist Dr. Michelle Moyer, a member of the team, was able
to leverage additional funding from the USDA Specialty Crops
Research Initiative to expand research and extension activities
to a four-year national project through 2022. Now called the
FRAME (Fungicide Resistance Assessment, Mitigation and
Extension) Network, the goal is to provide U.S. grape growers,
consultants and manufacturers with data and predictive tools to
determine the potential for fungicide resistance in vineyards and
help them better collaborate, design and implement management
programs for more effective PM control.
The main objectives of the FRAME project are:
* Identify where fungicide resistance currently occurs.
* Develop detection and monitoring tools.
* Improve fungicide application efficiency.


The Crush - April 2019

Table of Contents for the Digital Edition of The Crush - April 2019

The Crush - April 2019 - 1
The Crush - April 2019 - 2
The Crush - April 2019 - 3
The Crush - April 2019 - 4
The Crush - April 2019 - 5
The Crush - April 2019 - 6
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