Article by Matt Montgomery

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“Times are tight. Do I need to spend all that money on a soybean fungicide?”

That question has come up quite a bit in 2026. Commitment to fungicide on corn acreage runs high, but growers are not so sure about beans. There almost seems to be an underlying sense, an underlying “vibe,” that soybean fungicides are not necessarily the sure investment they once were. Where growers sense a lack of return, they seem to believe the issue is not simply a matter of low commodity prices and high inputs; they seem to suspect that the yield advantage itself just is not there.

So, what is a grower left to do? Should they stay the course, reduce treated acreage or exit the practice entirely? What might be a thoughtful approach?

Let’s begin by thinking about where we have been.

Fungicide use exploded in the mid-2000s following widespread concern over Asian Soybean Rust. The losses from that disease did not materialize and the industry began to experiment with pre-positioned fungicides. The results were impressive, but they seemed to be stronger in soybeans. Corn returns seemed to be a 50/50 proposition and soybean returns ran much higher. Data often indicated soybean returns in two-thirds of cases.

Why did we see that kind of return in soybeans?

To be honest, that remains a bit of a mystery.

The returns did not seemingly stem from soybean foliar disease suppression. While certain soybean-producing regions struggle with devastating late-season foliar disease, much of the central Midwest does not. Northern Illinois can see dramatic losses from white mold.  Extreme southern Illinois can see losses from frogeye leafspot. Central regions of the state, less prone to either disease, experienced similar yield advantages minus those diseases.

Other diseases were present, but significant losses from those diseases seem doubtful.  The impact of septoria, mildew, bacterial blight and soybean vein necrosis virus are too cosmetic in nature to fully account for the yield bump. Some of those are non-fungal pathogens, and fungicides would thus have no impact upon them. Sudden Death Syndrome, Soybean Cyst Nematode, late season phytophthora and recent additions such as Red Crown Rot cannot be managed by a foliar fungicide application.

If the response did not primarily come from disease suppression, where did it come from?  Theories behind that initial soybean fungicide response have varied.

This author has occasionally wondered if the respiration-reducing nature of strobilurin fungicides might tame soybean’s tendency to burn off sugars late season. That process is called photorespiration and strobilurin fungicides function by impeding respiration.

Others have speculated that strobilurins may impact ethylene production in the plant.  Ethylene is a naturally occurring plant growth regulator (PGR) that signals fruit to ripen (thus the reason a bad apple causes other apples to spoil nearby). That PGR also signals plants to mature. The experience of green stems following fungicide application may signal that the “ethylene theory” has some weight to it.

Fungicides may manipulate ethylene, causing plants to stay greener longer, giving pods more time to fill. It may be that, or, the benefits may stem from something else entirely.

There are many theories for why we saw yield advantages in beans, but to be honest, the explanation remains unsettled. If you ask five different agronomists for their take, this author suspects that you will get at least three or four different answers.

What does more current fungicide response data show?

Beck’s conducts a series of fungicide studies each season as part of our Practical Farm Research (PFR) program. Soybean fungicide studies are part of each season’s research work, and for two to three years, our research team has struggled to detect yield benefits.  These results have been significant enough that they have become a point of conversation among colleagues. Yet, the shadow of experience lingers on. An examination of plots that were sprayed with fungicide versus those that were not hints that something may still be occurring. Past experience indicates that an R3 fungicide application is still preferable for soybean fungicide returns.

So, what is a good recommendation?

Providing soybean foliar fungicide guidance is tricky for two main reasons.

First, we lack a solid theory that might explain why soybeans once responded so well. Was it disease? Is it decreased respiration? Did response stem from ethylene? Minus a solid theory, we have little guidance as to which acres might be more prone or less prone to respond to fungicide. It would be nice to have some kind of guidance for growers hoping to cut acreage. Without a theory, we cannot strategically reduce treated acres.

Second, we lack data to clearly guide growers. Yes, our PFR research has struggled to detect fungicide returns. Yet some kind of difference still seems to exist between treated versus untreated plots. Will our PFR trend hold? Has something fundamentally changed within soybean lines that decreases the yield bump associated with fungicides? Are there regional differences in soybean fungicide response that have gone undetected?  We simply do not know.

So, what is a grower to do?

One cannot blindly recommend a complete exit from fungicide use. Soybean fungicide applications displayed exceptionally strong responses over much of the past 20 years.  There still seems to be some kind of tangible difference between treated and untreated plots. That must be factored into any recommendation. Recent PFR work has failed to show equal returns. So, one cannot comfortably recommend maintaining the status quo. Future response is unknown, and unsettled theories mean that “well-educated guesses” are absent. Local data is desperately needed.

Growers are left with one option.

They should include periodic untreated check strips in the field for the foreseeable future.  Producers should reference those check strips and see if yield gains materialize. If benefits materialize, they should “stay the course” but continue to test. If yield gains consistently fail to materialize, the grower should slightly reduce fungicide applications during the following season. If yield gains consistently fail to materialize that next season, they can slightly reduce application again, etc.

A final thought.

Maintaining untreated test strips to gauge soybean fungicide returns may sound like a tedious process. It sounds like lots of work in an industry that already presses us for time.  However, fungicide investments are a significant input, and ROI is as tight as ever.  Determining fungicide returns is critical. Get those untreated test strips out there and get data for your farm to better guide future practice.