Fungal Pathogen Disease Management for Cold-Climate Wine Grapes in the Midwest
By Courtney Meeks, 2025 MMS Graduate Scholarship Winner
Wine Country in the Midwest
The Midwest is known for many things – unique accents, blizzards, and corn fields. However, many are unaware of the region’s growing grape industry. What started as a Wisconsinite’s fun project of breeding grapes has led to public releases of table and wine grape cultivars. It all started with a desire to grow grapes that could withstand our harsh winters while producing a harvest suitable for direct consumption or wine making.
The result was cold-climate interspecific hybrid grapes, a product of crossing native grapevines with Vitis vinifera (European wine grapes). Later research at UW–Madison demonstrated that not only can these cold-climate grapes tolerate our frigid winters, but they also inherited native fungal pathogen disease tolerance and potential resistance from the native grapes. This foundational research opened up an opportunity for researchers to begin tailoring disease management to these unique cultivars, rather than relying on data from highly susceptible V. vinifera cultivars. This is where my research started.
There are Five Common Fungal Pathogens of the Grape
- Elsinoe ampelina (anthracnose)
- Phyllosticita ampelicida (black rot)
- Plasmopara viticola (downy mildew; oomycete)
- Diaporthe ampelina (Phomopsis cane and leaf spot)
- Erysiphe necator (powdery mildew)
Left image: Frontenac Grapes
Right image: Blackrot Foliar
Control of these pathogens requires a combination of methods to ensure both environmental and financial health. This is referred to as an integrated pest management plan (IPM), or, specifically for diseases, the disease toolbox. When discussing these grape diseases, the most significant influence on disease development is the environment. One of the most important in-season tools for managing these pathogens is the use of fungicides. If the environment is highly conducive, the implementation of chemical control is crucial to protect both the harvest and vine health. My research aims to examine how fungicides are utilized in cold-climate vineyards to ensure our efforts at managing disease are sustainable and suited to our unique cultivars.
My First Research Project
My first research project spanned over two years. The primary objective of this study was to evaluate the performance of alternative spray programs in comparison to the current industry standard of calendar spraying. Essentially, a calendar system ensures fungicides are being applied at specific time intervals, 7 to 10 days or 10 to 14 days. While this method is easy, you have a date with your fungicide sprayer every week or so; you put it on your calendar and stick to the schedule.
I hypothesized this might not be ideal for these cultivars due to their ability to tolerate fungal pathogens. I compared this method of fungicide sprays to a reduction in overall fungicide application numbers as well as an organic fungicide program. These experimental fungicide spray programs were driven by our understanding of pathogen biology and the implementation of disease forecasting.
Both experimental treatments demonstrated outstanding potential for implementation by vineyards to optimize their fungicide spray programs! Of course, there are caveats and obstacles that vineyards need to be aware of before implementation. Still, through education and extension-based outreach, our lab is excited to see vineyards begin to transition to these alternative spray programs.
My Current Research Project
My current research project began last year. This project aims to examine the current state of fungicide resistance in Wisconsin vineyards. Quinone outside inhibitors (QoI) fungicides are classified as high risk for fungicide resistance development because they are a single-site mode of action, meaning they target one specific area in a fungus. By sampling single colonies of E. necator and P. viticola using stickers, I can bring these obligate pathogens back into the lab and molecularly examine the QoI target site.
Fungicide resistance can be attributed to genetic changes that correlate with partial or complete loss of sensitivity of a fungus to a fungicide. I inspect for the genetic mutation that is attributed to complete resistance, the G143A mutation, which occurs at amino acid 143 and changes the glycine (sensitive) to an alanine (resistant). We have some interesting preliminary trends for our 2024 P. viticola while I continue to troubleshoot the E. necator protocol. I am continuing to sample again this year, as well as conducting bioassays, which will allow me to examine the fungus genotype (glycine or alanine) in conjunction with its phenotype (sensitive or resistant) in the presence of a QoI fungicide.
Overall, my research goal is to provide insights from studies conducted on these unique cultivars to help Midwest vineyards make informed decisions for their vineyards. I hope my research provides concrete methods that vineyards can test and implement at their operations.
Above image: P. viticola
About Courtney Meeks
Courtney C Meeks is a fourth-year Ph.D. candidate in Dr. Leslie Holland’s Fruit Crop Pathology Lab at the University of Wisconsin–Madison. Her research is centered on addressing fungal disease problems for cold-climate grape growers. The cold-climate grape industry is relatively young, which presents opportunities to instill sustainable disease management practices. Cold-climate grapes are unique as their breeding has passed along native disease resistance genes.
Courtney’s research has exploited this trait by comparing organic and reduced-application fungicide programs to a standard commercial program in managing five common plant fungal pathogens: Diaporthe ampelina, Elsinoe ampelina, Erysiphe necator, Plasmopara viticola, and Phyllosticta ampelicida.
In addition, Courtney’s research is assessing fungicide resistance in Wisconsin vineyards. Fungicides are a critical tool for managing diseases in vineyards; however, their usage should be strategic to ensure efficiency and durability. The goal of all her research is to provide information to vineyards, specifically the relationship between their management strategies and grape fungal pathogens.
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