Many early-planted soybeans in the Midwest are somewhere in the R2 to R3 growth stages now, exhibiting excellent pollination success and ready for fungicide applications, according to Ken Ferrie, Farm Journal Field Agronomist.
Here are three quick reminders Ferrie and other agronomic advisers offer to help you make the call in this year’s soybean crop.
1. Weigh the financial pros and cons.
If your fields have little disease pressure this year, does it make sense to apply a foliar fungicide in soybeans? Probably in only a handful of scenarios, according to 2021 research by university Extension agronomists and pathologists published in Nature’s Scientific Reports.
The researchers determined 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 soybean production [only] when prices are near or above average.”
While some crop protection companies tout plant health benefits from making foliar fungicide applications to soybeans, agronomists say this is the year to carefully weigh a $35 to $40 per acre fungicide application against the potential payoff in yield per acre with $10-per-bushel soybeans.
2. Stage your soybean crop.
The sweet spot for foliar fungicide use is generally considered the R3 (beginning pod) growth stage. Look for that growth stage to be present in at least half of the field prior to treatment. Most years, the R3 growth stage will last approximately 10 days.
Learn how to stage your crop here.
Why treat at R3? Approximately 70% of a soybean plant’s yield comes from nodes 6 to 13. Many of the uppermost nodes of this region of the plant do not exist at R2 (full flower); therefore, a fungicide application this early has a limited impact on pod/seed retention and seed size, reports Beck’s Hybrids in this article.
“Conversely, at R4 (full pod), many of the lower nodes of this region are too far along in pod/ seed development for a fungicide to have a meaningful impact. Fungicide applications at R3 (beginning pod) work because the nodes that do the heavy lifting (6 to 13) are beginning pod development and are present at the top of the canopy at this time,” Beck’s says.
There are some reasons to treat soybeans at times other than R3.
For instance, the best foliar fungicide application timing for white mold at R1 growth stage (one open flower per plant on 50% of the plants), according to Michigan State University Extension.
In addition, applications made at R2 have performed well in recent research conducted in North Dakota.
3. Pick the right product for the job.
Determine what fungicide mode of action groups will provide the best efficacy to achieve maximum disease control, says Stephanie Porter, CCA and Illinois Soybean Association outreach agronomist.
Porter notes the North Central Regional Committee on Soybean Diseases has developed information on foliar fungicide efficacy for control of major foliar diseases. These efficacy ratings are based upon the level of disease control achieved by the product and are not necessarily reflective of yield increases achieved by the product application, she says.
4. Consider whether you need a herbicide rescue treatment.
OK, so that has nothing to do with addressing soybean diseases with fungicide, but here’s the deal: when soybeans are at R3 and you go after weeds you’re likely to lose some pods. Ferrie says to make sure your weed problems are worth treating now.
They very well could be, given how tough waterhemp pressure is in the Midwest this season.
“I am finally getting some reports of a lot better control with the second pass of Liberty, so conditions have changed in such we’re bringing down some pretty big weeds out there, but what a frustration,” he says. “Just be careful and stage your soybeans before you spray.”
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