Strategic management and timely fungicide applications significantly reduce the potential impact of frogeye leaf spot (FLS) in soybean fields. Instead of waiting for the disease to show up and potentially compromise crops, use the winter months to plan your approach to tackling FLS.
Effective fungicide use requires an understanding of field history, scouting and application timing. Note the following application guidelines:
How to prevent frogeye leaf spot in crops
Treatment and management of frogeye leaf spot should be based on field history and risk level, incorporating seed selection, fungicide application and crop rotation.
Seed selection
Several genes are commonly used for combating frogeye leaf spot. The Rcs3 gene is reported to be resistant to all known races of FLS pathogens in the U.S.¹ To set soybean fields up for success, a seed selection expert can provide more personalized guidance.
Frogeye leaf spot fungicide recommendation
Revytek® fungicide
When it comes to treating frogeye leaf spot, Revytek fungicide provides unparalleled power and proven plant health protection in a soybean fungicide. This fungicide provides a strong curative, fast uptake and long-lasting residual performance. This treatment boasts a +6-bu/A yield increase over untreated soybean fields thanks to its unique active ingredient, Revysol®, available only through BASF.
Revylok™ fungicide
A new soybean fungicide innovation from BASF, Revylok fungicide is designed for growers who are losing valuable bushels to disease. The complementary systemic effects of Revysol and Xemium® active ingredients are powerful against pathogens that have developed resistance.
Frogeye leaf spot fungicide application timing
The ideal treatment window for frogeye leaf spot is between R2 and R4, with early R3 being optimal for foliar application. It’s best to apply at least two to three modes of action to manage pathogen populations that have developed resistance to older chemistries.
Cultural practices
Crop rotation with nonhost crops like corn, sorghum and small grains can disrupt the life cycle of frogeye leaf spot, though it will require several growing seasons to greatly reduce the chance of infection. Reduced tillage systems also tend to have more instances of infection, since FLS overwinters in plant residue. Use of certified disease free seed will prevent seed borne infections.
Overcoming frogeye leaf spot fungicide resistance
Some infections are more fungicide-resistant than others. In the past, Group 11 fungicides have been widely used for managing FLS. However, since 2010, reports of FLS with resistance to Group 11 fungicides have increased across states like Nebraska and Iowa.
Professor Daren Mueller, a plant pathologist from Iowa State University, lists Group 11 fungicides as “high risk” because of their tendency to produce resistance. He goes on to classify DMI fungicides (Group 3) as “medium risk” and SDHI fungicides (Group 7) as “medium to high risk.”²
As mentioned above, a strong prevention and management plan will include several modes of action and a residual fungicide to provide a broad spectrum of control.
Keep an eye out for frogeye leaf spot
Frogeye leaf spot is one of many threats to soybean yield worth monitoring. Key takeaways:
- Scout early (R1) to identify signs of frogeye leaf spot.
- Treat early (late R2-R3) with a fungicide offering multiple modes of action.
- Be aware that FLS will not go away on its own, especially in a warm, humid climate.
Growers should check in frequently for updates on evolving diseases and resistances.
Experts are available to help you identify frogeye leaf spot and make a management plan. Reach out to your seed retailer, a nearby extension office agent, or your regional BASF representative.
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Endnotes
- Mangel, Dylan. “Frogeye Leaf Spot.” https://cropwatch.unl.edu/plant-disease/soybean/frogeye-leaf-spot/, CropWatch, 2021, cropwatch.unl.edu/plant-disease/soybean/frogeye-leaf-spot/. Accessed 19 Jan. 2026.
- Nahiyan, Abdullah, and Lindsey Thiessen. “Frogeye Leaf Spot of Soybean.” NC State Extension Publications, 8 Sept. 2020, content.ces.ncsu.edu/frogeye-leaf-spot-of-soybean-1. Accessed 19 Jan. 2026.
