Tom J. Bechman, Midwest Crops Editor
Agronomists in one camp insist that for maximum return on investment, you should go after top yields. That includes applying fungicides on soybeans, even without disease symptoms. Folks in the opposite camp are adamant that without disease symptoms, applying fungicides not only won’t provide a return on investment, but also could hasten development of resistance.
What do farmers say? Based on a recent Farm Futures survey of over 350 farmers nationwide, growers are split.
Survey question: Do you plan to apply fungicides on your soybeans this year?
Yes: 45%
No: 43%
No soybeans planned: 12%
A similar question was asked about applying fungicides on corn, and nearly 6 in 10 said they intended to spray fungicides. Of those applying fungicides, about 20% expected to make two or more applications.
What data says
Analyzing data from all over the Midwest is Shawn Conley’s specialty. The Extension soybean specialist at the University of Wisconsin, with others, used machine learning to summarize thousands of fungicide studies that published results in Nature.“Many earlier scientific studies did not find an economic return for spraying fungicides when there were no indications of disease,” Conley says. “However, our analysis suggests that, except for a few production environments located in the northern fringe of the U.S. north-central region, there was an economic benefit to using foliar fungicides in soybeans when prices are near or above average.”
Prices “near or above average” is key. When this study was done in 2021, soybean prices were considerably higher. Plus, the study emphasized that foliar fungicides should always be used judiciously in an integrated program that weighs their economic benefits against their environmental consequences.
With $10-per-bushel soybeans today, Conley notes that many applications are breakeven at best in the absence of pests. “Add in increased risk for pesticide resistance and how these applications may tie into human disease resistance questions, and I would be slow to pull the trigger [without disease symptoms],” Conley says.
What plant pathologists say
Damon Smith, plant pathologist at the University of Wisconsin, and Mandy Bish, plant pathologist at the University of Missouri, answered questions about spraying soybeans with fungicides as a prophylactic approach, without disease symptoms.Is a fungicide application recommended on soybeans whether you see disease symptoms or not?
Smith: No. As far as fungicide applications, plan on about 2 bushels per acre in yield response under no disease pressure. With a fungicide application costing between $25 and $30 per acre, it is hard to break even.
Under heavy white mold pressure, those odds change dramatically in favor of fungicide. We are looking at a new meta-analysis of the latest data to get at this with some new products, but the jury is still out there.
Bish: We rarely see disease pressure in soybeans in Missouri that warrants a fungicide application. We’ve conducted farmer-led strip trials across Missouri over the last several years, where farmers select products to test on their own fields. The average yield response has been 1.8 bushels per acre. It will be useful to learn if that yield difference changes with newer products.
Are there risks for resistance development from spraying fungicides where we don’t see disease?
Smith: Yes. Fungicide resistance is a huge risk when spraying in the absence of disease.
Bish: We can learn from our experiences with herbicide-resistant weeds. Unnecessary fungicide applications increase the risk of developing fungicide-resistant pathogens. Once resistance develops, there are no good in-season, nonchemical alternatives to help control disease outbreaks.
Are there legitimate risks to human health if fungicide resistance develops?
Smith: Yes. We can drive fungicide resistance in human pathogens, which is concerning.
Some fungicides claim other benefits like mitigating drought stress. Are these effects real? Do they justify application?
Smith: There are some plant health benefits outside of controlling diseases. As noted previously, data points to a 2-bushel-per-acre average advantage. However, these small benefits often won’t pay for the fungicide application, along with accounting for risk of pesticide resistance.
If you are spraying fungicides on soybeans, which is the best stage for spraying?
Smith: This depends on the disease and when it shows up. We developed forecasting tools to help answer: Do I need to spray? When is the best time to spray? Our national disease prediction tool can be found online. One feature at this site, hosted by the Crop Protection Network, is Bean Binoculars. This tool allows you to see specific disease reports from across the country, and to learn how to manage these disease incidents.
If you see disease, how do you know which product to apply and at what rate?
Smith: Use the Crop Protection Network fungicide efficacy tables or the interactive fungicide efficacy tool.
PFR Proven: Soybeans and fungicides
To make Beck’s PFR Proven list, a practice must show a positive yield gain every year while also averaging a positive return on investment over all three years in the Practical Farm Research program.Jason Gahimer, PFR program manager, notes that applying fungicides on soybeans is a PFR Proven practice. Here are more details:
PFR Proven fungicides. These fungicides have earned PFR Proven status: Miravis Top, Revytek, Stratego YLD, Trivapro, Lucento, Priaxor, Miravis Neo, Delaro Complete, Zolera FX and Delaro 325 SC.
ROI. Averaged over three years, the three fungicides with the best return on investment were Miravis Top at $48.21 per acre, Revytek at $27.35 per acre and Stratego YLD at $26.76 per acre.
Yield advantage. Averaged over three years, yield advantage ranged from 6.5 to 2.5 bushels per acre. The top three were Miravis Top at 6.5 bushels, Revytek at 4.6 bushels and Stratego YLD at 4.4 bushels.
Timing on growth stage. In seven-year, multilocation applications of fungicide and insecticide together, applying at R3 averaged $17.68 per acre. R2 lost $3.91 and R4 lost $2.53.
Time of day. Averaged over three years, spraying at 8 a.m. delivered $5.34 more ROI per acre than spraying at 3 p.m.
Carrier rate. Applying 20 gallons per acre of water was nearly $8 per acre more profitable than 15 gallons, and over $10 better than 10 gallons per acre in three-year testing.
