Are We Standing Out in The Field, Or Are We Outstanding in The Field?

With forthcoming EPA restrictions on broad-spectrum fungicides, the future of integrated grape disease management is evolving. Biofungicides are stepping into the spotlight—a surprising development even for me, a recently reformed traditionalist. Over the past five years, Cornell Grape Pathology has demonstrated that, when used correctly, biofungicides can offer season-long disease control equivalent to conventional chemistries. In this article, Dave teases some early results from new applied trials homing in on optimal biofungicide usage, digs into the archives to answer a question that’s been bothering him, and debuts Cornell Grape Pathology’s first “Outstanding in the Field” biofungicide recommendation list.

A Season of Change

Last spring, Katie and I published a prescient article on the future of grape disease management without broad spectrum fungicides, which among the other great tidbits of information that you find here, compared biological and conventional fungicides to electric vehicle and sports cars. I stand by that timely comparison- as both interest in EVs and new methods of grape disease control continue to rise. This is especially true considering proposed changes to mancozeb usage. You can read more about these changes, how they will impact grape production, and the results of our 2024 grower habit survey in Katie’s article.

I’m proud of our work over the past five years establishing that biofungicides can provide equivalent season-long disease control to conventional chemistries in our pathology vineyards. If you’d like to dig into our archives yourself, you can find our trial reports from 2020-2024 at the Gold Lab website: https://blogs.cornell.edu/goldlab/seasonal-fungicide-efficacy-trials/

All that said, the most common question we get from growers remains:

"How do I actually use them?"

This year, we're answering that question with five new applied trials—but thanks to support from the New York Wine and Grape Foundation, we got a head start during the 2024 growing season.

Welcome to the Arena: The Pathology Vineyards

The Cornell Pathology Vineyards in Geneva, NY, represent one of the toughest testing grounds for disease control. Across nine acres and nine concurrent disease trials, we deliberately manage these vineyards to promote disease, creating high-pressure environments ideal for rigorous fungicide testing. Our trials regularly have >100 unique combinations of conventional, biofungicide, and mixed rotational programs, and form the foundation of the NY/PA Grape Pest Management Guidelines. We share these results through articles like this one, talks at grower events and conferences, and peer-reviewed publications. In the pathology vineyards, our vines face what we call the "Big Three": powdery mildew, downy mildew, and black rot.

Our trials routinely see 100% damage in untreated controls. Add in documented fungicide resistance (Revus, strobilurins, phosphorous acid….), and our data represent the most challenging conditions imaginable.

Trial Spotlight: 2024 Biofungicide Application Timing Study

In 2024, we evaluated four mixed biofungicide-conventional programs targeting black rot, downy mildew, and powdery mildew in our New York Wine and Grape Foundation funded Traminette vineyard. Though we typically conduct PM and DM evaluations in our Chardonnay vineyard, we wanted to provide this trial with a bit more even playing field. We designed our experimental programs to target critical periods of disease control with different regimes of materials, and whether the choice of a conventional or a biomaterial was essential as to when it was used in the rotation:

Treatments differed in the timing and placement of biofungicides versus conventional chemistries:

Biofungicides early, then conventional (B, C, B, C)
Conventional early, then biofungicides (C, B, C, B)
Biofungicides at critical control window, bounded by conventional (C, C, B, B, C, C)
Conventional at critical control window, bounded by biofungicides (B, B, C, C, B, B)

Applications followed standard phenological timing, with the "critical control" window defined as a 4–5 week range from immediate pre-bloom to bunch closure. As always, we included an untreated control treatment of equal size and replications.

There were no significant differences in disease control between any of the programs. All treatments significantly outperformed the untreated control. Powdery mildew was virtually undetectable on the moderately resistant cultivar 'Traminette', while black rot and downy mildew remained present. These findings suggest biofungicides may be used interchangeably with conventional fungicides within mixed rotations during key periods of disease pressure.

bar chart with 5 treatments and 3 diseases, so 15 bars total

Figure 1: Cluster (a, top), and foliage (b, bottom), damage results as compared to the untreated check, indicated biofungicides can be used interchangeably with conventional fungicides.

Looking Back: 5 Years of Data

Skeptical? So was I. So I dug through five years of powdery and downy mildew data on Chardonnay. I categorized treatments into three groups:

Biofungicide-only programs
Conventional-only programs
Mixed programs with 2+ biofungicide applications

Across both cluster and foliar evaluations, mixed programs performed equally well as conventional-only programs and significantly better than the untreated controls. Rotational programs incorporating 2 or more biological fungicides provided equivalent foliar and cluster mildew control to conventional only programs.

bar chart w/ 3 spray programs & amount of disease; 6 bars total

Figure 2: Comparison of biofungicide and conventional rotational programs to conventional only programs over a 5-year period showing that they are equally effective in controlling downy mildew (a, top) and powdery mildew (b, bottom) on both fruit and foliage.

Notably, the best-performing mixed programs:

Included about 5 biofungicide applications per season
Alternated biofungicides every other spray
Used biofungicides either throughout or specifically during critical control periods

We still have more digging to do, but we are excited by these preliminary findings These supporting the case for reducing synthetic chemistry use without compromising disease control or yield potential.

bar chart: 14 bars, coupled, with left (blue) for cluster and right (orange) for foliar

Figure 3: Comparison of biofungicide and conventional rotational programs to the untreated control over a 5-year period showing efficacy against downy mildew (a, top), and powdery mildew (b, bottom) on Chardonnay grapes according to the number of biofungicides applied.

Our Top Picks: Biofungicide Recommendations

After five years of field testing, we’re proud to share our first "Outstanding in the Field" biofungicide recommendation list—based on replicated trials, field observations, and a little intuition. What started as a joke of me literally standing out in the field has now become a genuine list of recommendation! However, I would like to emphasize that this list is not a substitute for the label. Trade names are used for convenience only, and no endorsement is intended for the products mentioned, nor lack of endorsement for products not mentioned. Always read the label to ensure lawful use.

Chart, plus man standing out in vineyard with hands raised above head

Visit the Pathology Vineyards, or have us come visit you!

Our vineyards are open to the industry each fall on the first Wednesday after Labor Day. Growers, chemical reps, winery staff, and researchers are welcome. Email us to be added to the invitation list! If you have any questions regarding this research, please feel free to reach out to Katie or myself, we are happy to chat or email. We would also encourage you to invite us to your vineyards, whether you’re experiencing an issue you cannot seem to figure out, have an anomaly that should be noted, just want to see our smiling faces, we would like very much to hear from you.

Dave Combs – dbc10 [at] cornell.edu
Dr. Katie Gold – kg557 [at] cornell.edu

About the author: Dave Combs is a Research & Extension Support Specialist II in Dr. Katie Gold’s Grape Pathology Laboratory at Cornell AgriTech in Geneva, New York, with 20+ years of experience in chemical and cultural grape disease management. He runs Cornell Grape Pathology’s annual fungicide efficacy evaluation program. These trials challenge conventional, biological and mixed fungicide programs against five common grapevine diseases in the 9+ acre Cornell pathology vineyards.