Project Title: Monitoring and Mapping Grape Powdery Mildew Fungicide Resistance and Crown Gall Incidence in Washington Vineyards

Project Duration: 3 years, FY18-20, 1 July 2017- 30 June 2020

Principal Investigator(s): Michelle Moyer, Assistant Professor
Organization: Washington State University
Address: 24106 N. Bunn Rd., Prosser, WA 99350
Telephone: 509-786-9234

Collaborators: Dr. Walt Mahaffee
Organization: USDA-ARS, Horticultural Research Unit
Address: 3420 NW Orchard Ave., Corvallis, OR 97330
Telephone: 541-738-4036


This two-part project collected baseline survey data on two important issues in Washington wine grape production: 1) the presence of fungicide resistance in grape powdery mildew to one of our main class of synthetic fungicides, and 2) continued outbreaks of crown gall in newly planted vineyards despite recent industry-wide educational efforts on the importance of planting certified vines.

The development of fungicide resistance results in substantial economic loss related to fungicide application labor costs and unmarketable fruit . Working with a national team, we have developed a rapid diagnostic test to determine the presence of a genetic mutation that confirms resistance to the strobilurin (QoI, FRAC 11) fungicides to the grape powdery mildew fungus. We coupled this rapid testing tool with improved scouting and collections methods. The key outcome from this objective is the confirmation that fungicide resistance is here and is widespread. While fungicide resistance was a likely culprit in the wide-spread disease outbreaks seen in recent years, other factors that contribute to program failure and fungicide resistance selection were noticeable. These factors include: poor spray timing, lack of fungicide rotation, and poor sprayer application. To effectively manage fungicide resistance in grape powdery mildew, we will not only need to focus on chemical product stewardship, but also re-focus on product application and cultural approaches to reduce disease pressure.

Grapevine crown gall, a serious disease in northern climates, can be a limiting factor to successful vineyard establishment. Protocol 2010, which is the foundation for the vine certification process in the US, has approaches that reduce the crown gall pathogen in vines. However, not all vines on the market are certified, and recent (last 15 years) expansion of the industry resulted in wide-spread planting of vines from many sources. It became very clear through this study that many growers are not aware of what “certified” means for planting materials. For most of our surveyed sites, people assumed that the nursery was the certification unit, not the planting material (inaccurate assumption). It was also clear in our scouting efforts that, crown gall does serve as an indicator for site appropriateness (i.e., risk of cold damage) for wine grapes. While this was not always a welcomed observation, sites suffering from extreme levels of crown gall were often planted poor locations prone to cold damage. Typically, poor site selection was generally coupled with the choice to use non-certified vines. In these recent expansions, the choice to plant soon was the primary driver for material selection, rather than the choice to plant “clean”.

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Pest & Disease // Viticulture //