Life After Broad Spectrums … Can We Survive?

Plant Pathology and Plant-Microbe Biology Section
Viticulture and Enology
Crops

EPA restrictions against broad-spectrum pesticides are imminent. What does that mean for the future of Eastern grape production? Dave Combs, research support specialist in Dr. Katie Gold’s Grape Pathology Laboratory at Cornell AgriTech, shares his take on what grape disease management will look like in a post-broad-spectrum world.

Going the way of the dodo

In early December 2023, the EPA announced to a small stakeholder audience over Zoom what many of us in the industry consider to be the first in a forthcoming series of restrictions on broad-spectrum pesticide use. Despite the public comments received during a 2021 review period, the EPA is deregistering (aka canceling) all conventional crop use of Ziram (as well as Thiram and Ferbam) beginning in 2026.

The EPA regularly reviews pesticide registrations. This process determines what crops are allowed to use what chemistries and to what extent. Both Captan and Mancozeb are due to begin this process in 2024. It is likely that grape growers’ ability to use these materials will be significantly reduced or outright withdrawn.

Things are changing and changing rapidly. In the future, materials we have traditionally built grapevine disease management programs around will be less available, if at all. Milder winters will increase overwintering disease pressure. Some think that this will mean the end of Northeast grape production, but is that truly the case?

Are the good ol’ days behind us?

Every generation thinks it has advantages over the last, and yet every generation yearns for the “good ol’ days.” For example, many of us still pine for the era of big muscle cars, V8 engines, and the days when a gallon of gas cost only $1. Yet, that hasn’t stopped us from making the swap to electric vehicles for family and farm use. Sure, an electric engine just doesn’t have the presence of a 4-barrel carburetor sucking down leaded fuel at 8 miles to the gallon, and it certainly is an adjustment to have to schedule a mid-trip car charging break on long drives, but you can’t deny that an EV runs laps around those old behemoths when it comes to gas expense, benefit to the environment and carbon credits.

This is a surprisingly accurate metaphor for the grape disease management situation we face. We may be losing the old V8s because of compounding environmental and health issues, but fortunately for us, there are effective electric vehicles just waiting to be picked up on the lot.

The choice is yours: either put in that charging station or keep doing burn outs at stop lights.

The future is calling

The agrichemical industry has prepared for these forthcoming changes. In recent years, even the stoutest conventional chemistry manufacturers have jumped to develop new modes of action and biofungicides. Some were a little more ahead of the curve than others, but nonetheless, everyone seems to be on the same road now. And fortunately for grape growers, we are well past the days of the Prius being the only EV on the lot and are solidly in our Tesla era.

I run Cornell Grape Pathology’s fungicide efficacy evaluation program, which includes five unique disease trials that span 9 vineyard acres. Our trials regularly have well over 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, Dr. Gold’s annual “manifesto” (aka her Annual Disease Control Update) and peer-reviewed publications. These trials are the hardest arena any chemistry, conventional or biological, will ever go up against as they are intentionally managed to encourage disease development.

man with red shirt and woman with hat standing in a field — Dave Combs (left) runs Cornell Grape Pathology's Fungicide Efficacy Evaluation Program. Dr. Katie Gold and Dave (right) evaluating Chardonnay clusters for downy mildew severity.

Dave Combs (left) runs the Grape Pathology Laboratory's fungicide efficacy evaluation program and has 20+ years of experience testing agrichemicals for disease and insect control. Dr. Katie Gold and Dave (right) evaluate Chardonnay clusters for downy mildew severity.

I have been testing agricultural chemicals since before cellphones were the norm. I remember testing early formulations of kaolin clay at 50 lbs/A, or more accurately, I remember the absurd amount of ethanol I had to use to clean that sludge out of my equipment. I was not exactly excited when we first started receiving “untraditional” products to test.

Believe me when I say no one is more surprised than me to discover I’ve become a biological fungicide enthusiast!

Every year since 2019, we have seen an increase in the number of new chemistries, both conventional and biological, from new and traditional agrichemical players in our trials. In 2023, new biological products outnumbered new conventional products in our trials by a factor of 5 to 1! In 2022, Dr. Gold and I published an Appellation Cornell article introducing some of these new biological materials, their unique modes of action in comparison to traditional chemistries, and some preliminary efficacy findings.

Most of these materials have comparable label rates to the old ones we’re used to, and some are even lower. In addition to being much safer for human health and the environment, I have found them to be easy to work with, requiring far less PPE and applicator caution. A huge bonus is that biofungicides are unlikely to have resistance develop due to their unique modes of action in comparison to conventionals. But most importantly … THEY WORK!

However, just like the electric car, we must make lifestyle adjustments to get the best performance.

Getting the best bang for buck

Let’s continue with the car metaphor. Think of your pesticide shed as your home garage: There should still be 2 bays. We don’t want you to get rid of the muscle car; we want you to consider only driving it on Sundays.

Over the course of four-plus years of testing, we have found that biological materials are most effective when they are used in rotation with traditional chemistries. We recommend preserving highly effective conventional material use for critical control periods and severe disease conditions, while otherwise rotating between conventional and biomaterials.

four charts that show incedents and severity — Data from the Cornell Grape Pathology’s powdery mildew (PM) and downy mildew (DM) trials.

Data from the Grape Pathology Laboratory’s powdery mildew (PM) and downy mildew (DM) trials. Remember our trials are the hardest arena any chemistry will ever face! Control programs that rotate biopesticides with conventional chemistries (such as Lifegard+Zampro [left] and Lifegard+Vivando [right]) can provide statistically and numerically similar levels of control to conventional only programs. From Paul et al. in review.

It is no secret that the New York grape industry struggles with fungicide resistance. By reducing powerful conventional material use frequency via rotation with biologicals, we are also preserving and lengthening their active lifespan for effective disease control.

Our current data suggests that biopesticides should be used first when in rotation with traditional chemistries. However, because this is such a new frontier, we are still learning what conventional and biological materials pair best with each other and at what application timings.

We’ve been busy at Cornell Grape Pathology planting new vineyards so that we may seek the answers to these questions. In 2021, the New York Wine and Grape Foundation awarded us a sustainability grant to plant a 1-acre Traminette pathology vineyard at Cornell AgriTech in Geneva, New York, to serve as a biopesticide trial home base to evaluate application timing and tank mix combos. The 2024 season will be the first year of this trial, and we look forward to sharing the results.

In 2023, we joined VitisGen3, the third renewal of a highly successful USDA NIFA Specialty Crop Research Initiative. That spring season we planted two new vineyards of multiple highly promising varieties with innate powdery mildew and downy mildew resistance developed over the project’s previous 10-year span. These grapevines produce European variety quality wines with resistance genes from diverse Vitis species. Once these vineyards come to maturity, we will use them to design ideal spray programs that combine conventional and biologicals to best preserve their innate resistance.

In the meantime, until we have more data on how biological and conventional active ingredients impact one another, we suggest you avoid tank mixing biopesticides with conventional products or other biopesticides, unless specified by the manufacturer. The reasoning behind this is simple: Some biopesticides contain live agents that are reactivated when added to water. By mixing them with a material designed to kill live agents (e.g., a conventional, or even another, biopesticide), we may be wasting money, material and time by inactivating the biological before it reaches the nozzle.

But what to do in the meantime?

Ziram has a broad activity spectrum against phomopsis, black rot and downy mildew and will be a sad loss, especially for Concord growers. However, there are both biologicals and conventional materials showing great promise that will likely be acceptable replacements.

Phomopsis trials have been difficult to manage, and we have not yet been able to gather any useful data with any material. Always wrong year, wrong vineyard. We’re trying again in the 2024 season so keep your fingers crossed for us. In the meantime, we still have manzate available. The PHI and max amount/A are always concerning, however there are some others that will likely prove efficacious. Several copper formulations, both conventional and organic, are effective for Phomopsis control. Cornell Grape Pathology has been testing a low dose formulation in development by a Geneva, New York-based startup that shows great promise and hopefully will be available in 2025. Ecoswing, Theia, Howler EVO and Lifegard are all biofungicides that will likely have some effect on this pathogen. Conventional options with probable but unproven activities are Aprovia, Cevya, Mettle and Miravis Prime.

We have conducted black rot trials in our Niagara vines for the past three years. Biofungicides have done very well against this pathogen and in some seasons are standout treatments– in particular, a tank mix of Stargus, a living agent, and Regalia, a plant extract. Yes, I did just say not to tank mix, but hear me out: These are two materials that were intentionally designed to complement each other in the tank. The living material that comprises Stargus was specifically selected for its performance in the presence of the plant extract that makes up Regalia. Lifegard consistently has been effective, and Howler’s new EVO formulation has also done well. Across all three years of our black rot trial thus far, Aprovia 0.83EC has consistently provided the best cluster and foliar protection. Other conventional materials that have provided satisfactory black rot control in our trials include Cevya, Mettle, Rhyme and Rally.

Biofungicides against downy mildew have been tested for quite some time, and unfortunately there hasn’t been a panacea. With the resistance issues of FRAC’s 40 and 11, coupled with potential phosphorous acid tolerance, this could prove to be a troublesome issue soon. Again, we find that Lifegard provides consistent, commercially acceptable downy mildew control. Romeo, a product with similar mode of action but a different active ingredient, has also performed satisfactorily. In 2023, Howler EVO (the new formulation) and Theia performed exceptionally. Certis has acquired both materials from their former manufacturer, and both will be available for use in the 2024 season. Some conventional materials remain effective. Ranman worked well in our trials, especially when tank mixed with a phos. acid. Zampro is composed of two active ingredients, one of which is a FRAC 40, but the other component is a FRAC 45 and still very effective. Ridomil is still highly effective against downy but limited to one application per year and should not be used as a rescue material.

Final thoughts

Think of a racetrack. On its own, the Tesla can give a racecar a run for its money but probably not beat it. But if you give it a head start and a pristine track … now we’re talking!

The same is true for biological fungicides. It is imperative that you provide your biologicals the best starting environment possible for them to succeed. Keep your canopy in check for best spray coverage and penetration. This has the added benefit of improving airflow and reducing disease development risk. Calibrate and pattern your sprayer, use enough water per acre to get proper coverage and use the proper materials at the proper rates.

Given their unique modes of action, such as defense activation, biofungicides have a low resistance profile; however, this is something that we should not push to find out. Rotate modes of action/FRAC groups every application. Make no more applications per year than the label allows. Personally, I don’t like to use any one MOA more than twice a season, be it biological or conventional, but I know reality doesn’t always shadow research.

Without broad spectrums, there will be more use pressure on the remaining available conventionals, which could lead to fungicide resistance development. Not good. To prevent this, save the ‘hot rods’ for when they are most needed in the critical control periods and otherwise rotate between biologicals and conventionals.

As a long-term solution, consider planting newly released grapevine varieties that have more innate resistance than European-only grapevines, such as historical releases from Cornell Grape Breeding like Traminette, and new releases from VitisGen3 as they become available. Future results from our VitisGen3 variety trial will help us all better understand how and when to use biofungicides for effective disease control.

So, will there be life after broad spectrums? YES, I do believe there will be. But just as we’ve seen with electric cars, you will have to make some lifestyle changes and take some extra steps to accommodate their quirks to ensure you’re getting the best performance possible. Vroom vroom – the future is calling!

Dave Combs is a research support specialist 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. Dave can be contacted via email at dbc10 [at] cornell.edu (dbc10[at]cornell[dot]edu).