Historically, foliar diseases have been a major threat to soybean producers in southern states, and that threat has been realized even more in the last 10 years, where losses due to foliar diseases had an estimated peak of nearly a $22 per acre loss in 2018 (Fig. 1). A similar trend also has been observed in northern states, where there was an estimated peak of nearly a $16 per acre loss in 2018 due to foliar diseases (data not shown, Crop Protection Network).

In response to the increasing threat of foliar diseases, an increase in foliar fungicide use in soybean has occurred the last several years in the U.S. Partly due to this increased use, some important pathogens have developed resistance to commonly used fungicides. Most notable is the frogeye leaf spot pathogen (Cercospora sojina), in which strobilurin fungicide-resistant strains have been detected in over 20 states, which span from the Canadian border to the Gulf coast to the Atlantic coast. In addition, pathogens that cause Cercospora leaf blight, Septoria brown spot, and target spot also have developed resistance to important foliar fungicides used on soybean.

While foliar diseases have become more important, marketing and advertising of foliar fungicides have also increased. Oftentimes, the marketing campaigns highlight the potential “yield increase” from the use of fungicides but may not focus much on actual disease management and how to effectively use the products as part of an integrated pest management program. In addition to the threat of plant pathogens becoming resistant to fungicides, resistance can spill over into human and animal health. An important human pathogen of health-compromised people, Aspergillus fumigatus, has developed resistance to triazole fungicides used in human health. Triazole fungicides are also an important group routinely used on soybean to manage foliar diseases. Recent research by Kang et al. (2021) indicated a potential association between triazole-resistant strains of A. fumigatus and use of triazole fungicides in agricultural settings. This topic was recently taken up by a committee of the National Academies of Sciences, Engineering, and Medicine and was discussed at a public workshop series on Antimicrobial Resistance in June 2022.

Potential implications of increased fungicide use over millions of crop acres are being discussed by the medical community and other groups outside of agriculture. Meanwhile, few tools have been developed to help soybean farmers make the most-informed foliar fungicide application decisions based on disease prediction. It is critically important that disease prediction tools that will help farmers make fungicide application decisions be developed and expanded. Such tools will benefit production and profitability of farms, while also reducing the potential risk of exposing both plant pathogens and human pathogens to fungicides that could lead to the selection of fungicide-resistant strains.

The Sporecaster prediction tool (Willbur et al. 2018), developed by the Damon Smith Laboratory at the University of Wisconsin through support from soybean checkoff funds, has been successful in helping farmers in northern states make fungicide application decisions for management of white mold (Sclerotinia stem rot). A recent project initiated in 2021 and funded by the North Central Soybean Research Program (NCSRP), led by Damon Smith (“Multidimensional approaches for improved productivity, sustainability, and management of major soybean diseases in the North Central U.S.”) is adapting the Sporecaster framework to develop and validate prediction tools for frogeye leaf spot. Our work on the current “Multi-Regional” project in years 1 and 2, has successfully expanded the NCSRP project to the Southern, Midsouthern, and Atlantic regions, and provides an opportunity for soybean pathologists across the nation to collaborate with each other and develop and validate tools for prediction of frogeye leaf spot as well as Cercospora leaf blight and target spot. A released beta version of the “Frogspotter” app for frogeye leaf spot prediction showed promising results in field validation trials across the U.S. in the 2023 and 2024 growing seasons. Ultimately, these tools will provide validated resources that farmers across the U.S. can utilize to make important disease management decisions.

Overall Goal: To develop improved management strategies, and communication of those strategies, for the sustainable management of soybean diseases that affect multiple production regions across the U.S.
Objective 1. Expand the development and validation of frogeye leaf spot prediction tool to new regions, using the Sporecaster framework
Objective 2. Develop and conduct experiments to adapt the Sporecaster framework for Cercospora leaf blight prediction
Objective 3. Develop and conduct experiments to adapt the Sporecaster framework for target spot prediction
Objective 4. Communicate results of the research to farmers and other stakeholders involved with soybean production

• Peer-reviewed publications that detail the development of prediction models and tools for Cercospora leaf blight, frogeye leaf spot, and target spot
• Peer-reviewed publication that reports on the most efficacious and economically viable fungicides for management of Cercospora leaf blight
• Peer-reviewed publication that reports on the most efficacious and economically viable fungicides for management of target spot
• Peer-reviewed publication that detail the geographical and temporal distribution of spores of important foliar fungal pathogens of soybean that will improve our epidemiological and biological understanding of these pathogens
• Updated foliar disease information on SRIN
• Updated Extension publication on Frogeye Leaf Spot and new Extension publications on Cercospora leaf blight and target spot

Updated July 31, 2025:
Uniform foliar fungicide trials have been planted at 15 locations across 11 states (AL, AR, DE, KY, LA, MS, NC, PA, TN, VA, WI). Growth stages at these locations range from V4 to R3. Due to frequent spring rains, many of the locations were planted later than normal. Frogeye leaf spot has been observed at many of the locations already, which should help provide for excellent fungicide efficacy comparisons among products. At 13 locations, spore traps have been deployed at two different heights within a “no fungicide” area of the field. The spores are being collected weekly throughout the season and are being analyzed via molecular quantification assays at the University of Wisconsin (Damon Smith Lab) and at Louisiana State University (Sara Thomas-Sharma Lab). Assays quantifying the frogeye leaf spot pathogen (Cercospora sojina) and the pathogens that cause Cercospora leaf blight (C. flagellaris C. sigesbeckiae, and C. kikuchii) from spore trap samples collected during the 2024 season are nearing completion. The data from these assays are being used to validate disease forecasting systems and to better understand the basic epidemiology of these important soybean diseases. The frogeye leaf spot forecasting system is now publicly available for farmers and others to use, as part of the Crop Protection Network’s Crop Disease Forecasting tool. The frogeye leaf spot forecasting system will help soybean farmers make critical soybean disease management decisions within the season and is the first of its kind to be publicly available. So far, this has been the largest success achieved by this project.

Updated January 31, 2026:
Uniform fungicide trial:
Uniform soybean foliar fungicide field trials were conducted in nineteen different states during the 2025 growing season (data from two projects were combined, where 11 states participating as collaborators in this project, and 8 states participating through a different regional project), in which fourteen treatments and a nontreated check were evaluated. In total, fourteen treatments were evaluated, which included a nontreated control. All fungicides were applied at the R3 growth stage (beginning pod), except for a few treatments that were applied at the R5 growth stage (beginning seed) or applied twice at R3 and R5.

Data from 22 field sites have been statistically analyzed so far. Across these 22 sites primary disease pressure came from frogeye leaf spot (FLS; caused by Cercospora sojina) and Septoria brown spot (SBS; caused by Septoria glycines). All treatments except Oxidate reduced FLS severity compared to the nontreated control, and all treatments except Badger, Affiance, “generic Quilt” (R5), and Oxidate reduced SBS severity compared to the nontreated control. Averaged across all locations, only plots treated with Affiance (R3), Delaro Complete (R3+R5 and R5 alone), “generic Quilt” (R5), Oxidate, Viatude, Miravis Top (R3+R5 and R5 alone) resulted in a significantly greater yield than the nontreated control.

The data from the uniform fungicide trial are being used to help revise the 2026 edition of the Crop Protection Network Soybean Foliar Fungicide Efficacy Guide. In addition, the data from these trials are being used to test, adjust, and optimize disease prediction models.

Spore trap network and quantification of foliar soybean pathogens:
Spore traps were deployed in soybean fields across thirteen different locations in 2025. Spore samples were collected at two different heights weekly. The samples were sent in bulk to the Smith Laboratory (University of Wisconsin), where DNA currently is being extracted from the 2025 spore samples. For the spore samples collected in 2023 and 2024 (3,339 trap samples in total), all DNA have been extracted, and the Smith Lab is developing an assay to enumerate spores of Cercospora sojina (FLS pathogen). The Thomas-Sharma Lab (LSU) has developed assays to enumerate spores of the species of Cercospora that cause Cercospora leaf blight and spores of the target spot pathogen (Corynespora cassiicola).

For detection of C. cassiicola, initially six DNA samples from Dr. Carl Bradley’s lab (University of Kentucky) of C. cassiicola were used to evaluate a primer that was developed previously by Ciampi-Guillardi et al. (2020). Both conventional and quantitative PCR (qPCR) was used to amplify the samples. Following this, six additional DNA samples were received from Dr. Alejandro Rojas’ lab (Michigan State University) and were also used to perform the qPCR using the same primers, making a total of 12 DNA samples. Once USDA-APHIS permits were received, the Thomas-Sharma Lab was able to receive 23 isolates from Dr. Bradley’s and Dr. Rojas’ laboratories. These isolates are currently being used for spore production and validation of the same primers for use on spore trap samples.

For detection of species of Cercospora that cause Cercospora leaf bligtht, DNA samples from spore traps deployed in 2023 and 2024 were used in the Thomas-Sharma Lab in duplicate to detect C. cf. flagellaris, C. cf. sigesbeckiae, and C. kikuchii using in house qPCR assays. A primary finding of this study is although CLB is not generally an economically damaging disease in northern soybean growing regions of the U.S., spores of the pathogens are present in most states. This suggests that a combination of environment and host genetics is likely to limit the impact of the pathogen in northern states.

The specific findings by year are shown below:
2023:
• A total of 1032 DNA samples were received
• The DNA samples were from 20 states: Alabama, Arkansas, Delaware, Florida, Iowa, Indiana, Kentucky, Louisiana, Michigan, Mississippi, Missouri, North Carolina, North Dakota, Nebraska, Ohio, Penssylvania, Tennessee, Virginia, Wisconsin and Minnesota.
• There were differences in the species detected in different states:
o None of the species was detected in Minnesota
o Only C. flagellaris was detected in Alabama, Florida, Mississippi, Ohio, Virginia, Wisconsin, Michigan, and North Dakota
o C. flagellaris and C. kikuchii were detected in North Carolina, Arkansas and Tennessee
o C. flagellaris and C. sigesbeckiae were detected in Iowa, Louisiana, Missouri, and Delaware
o C. flagellaris, C. sigesbeckiae, and C. kikuchii were detected in Indiana, Kentucky, Pennsylvania, and Nebraska
• Overall, C. flagellaris (77%) was the predominant species detected across all spore trap samples, followed by C. sigesbeckiae (16%) and C. kikuchii (7%).
• C. flagellaris reached the highest spore numbers. For all three pathogen species, it was common to detect Log10 3-5 (1000-100,000) spores.
• There were differences in the pattens of spore detection during the season in different states. In Wisconsin and Michigan spores were detected earlier in the season, while in Delaware and Florida, spores were detected towards the end of the season.

2024:
• A total of 1138 DNA samples were received
• The DNA samples were from 20 states, viz; Alabama, Arkansas, Delaware, Illinois, Iowa, Indiana, Kentucky, Louisiana, Michigan, Mississippi, Missouri, North Carolina, North Dakota, Nebraska, Ohio, Penssylvania, Tennessee, Oklahoma, Wisconsin and Minnesota. Note that this year, no samples were received from Florida and Virginia, but samples were obtained from Illinois and Oklahoma.
• There were differences in the species detected in different states, but the pattern was different from 2023. Spores were detected in Minnesota in 2024. Other specific observations include,
o C. sigesbeckiae was detected in all 20 states
o C. flagellaris was detected in 19 states except Oklahoma
o C. kikuchii was detected in 13 states but not in Arkansas, Indiana, Minnesota, North Dakota, Nebraska, Ohio, and Wisconsin.
• In 2024 as well majority of the spore trap samples had C. flagellaris (50%), while C. sigesbeckiae (36.9%) and C. kikuchii (12.3%) was detected at lower levels.
• In 2024, C. sigesbeckiae reached higher numbers more frequently than C. flagellaris which remained in the Log10 3-4 (1000-10,000 spore) range more frequently.
• Unlike 2023, spores were detected throughout the season in Wisconsin and Michigan. Similar to 2023, most spores in Delaware were detected towards the end of the season.

Predictive modeling of soybean foliar diseases:
The greatest success in this area was the launch of the frogeye leaf spot model that was available for use in the 2025 growing season. This tool is available on the Crop Protection Network website (https://cropprotectionnetwork.org/), and has a user-friendly interface where multiple fields (locations) can be added to monitor risk during critical stages (typically between R1 and R5 growth stages). Soybean farmers across the U.S. are now able to utilize this tool to help them make better informed decisions for management of frogeye leaf spot. The frogeye leaf spot risk tool continues to be validated through field trial protocols that are being conducted across multiple states where FLS risk thresholds of 40%-60% are being evaluated as “triggers” for fungicide application. So far, these validation trials have shown that the risk tool has been accurate in predictive FLS risk across a large geography. In addition to the FLS risk tool, the initial building blocks have been assembled from this project for subsequent development of risk models for Cercospora leaf blight and target spot.

Abstracts presented at scientific meetings in 2025:
Dalha A. I., Allen, T.W., Amie, J., Betts, A.K., Bish, M., Bond, J.P., Bradley, C.A., Chilvers, M.I., Collins, A.A., Doyle, V.P., Esker, P.D., Fakhoury, A.F., Faske, T.R., Hyzer, L., Jimenez Beitia, F., Kelly, H.M., Langston, D.B., Lopez-Nicora, H., Malvick, D.K., Mangel, D., Mathew, F.M., Mueller, D.S., Price, P.P., Richardson, A., Rojas, J.A., Sikora, E.J., Small, I., Smith, D.L., Telenko, D.E.P., Webster, R.W., Wilkerson, T., Yerukala, S., Richards, J.K., Thomas-Sharma, S. 2025. Exploring airborne inoculum of Cercospora spp. and Corynespora cassicola in soybean fields across the U.S. Annual Meeting of the Southern Soybean Disease Workers, Pensacola Beach, FL, February 26, 2025.

Dalha A. I.., Allen, T.W., Amie, J. , Betts, A.K., Bish, M., Bond, J.P., Bradley, C.A., Chilvers, M.I., Collins, A.A., Doyle, V.P., Esker, P.D., Fakhoury, A.M., Faske, T.R., Hyzer, L., Jiménez-Beitia, F. E., Kelly, H.M., Langston, D.B., Lopez-Nicora, H.D., Malvick, D.K., Mangel, D., Mathew, F.M., Mueller, D.S., Price, P.P., Richardson, A., Rojas, J.A., Sikora, E.J., Small, I. M., Smith, D.L., Telenko, D.E.P., Webster, R.W., Wilkerson, T., Yerukala, S., Richards, J.K., and Thomas-Sharma, S. Investigating the timing of airborne conidia of Cercospora spp. in soybean fields across twenty states in the U.S. Plant Health 2025 (American Phytopathological Society Meeting), Honolulu, HI, August 2-5, 2025.

Gonzalez-Acuna, J. F., Allen, T. W., Bish, M. D., Bradley, C. A., Camiletti, B. X., Dangal, N. K., Fakhoury, A., Faske, T. R., Kelly, H. M. Y., Lopez-Nicora, H., Lux, L., Malvick, D. K., Mangel, D., Markell, S. G., Mueller, D. S., Scherer, J. M., Sikora, E. J., Price, P. P., Sattler, J., Smith, D. L., Telenko, D. E. P., Webster, R. W. 2025. Annual Meeting of the Southern Soybean Disease Workers, Pensacola Beach, FL, February 26, 2025.

Gonzalez-Acuna, J. F., Allen, T. W., Bish, M. D., Bradley, C. A., Camiletti, B. X., Dangal, N. K., Fakhoury, A. M., Faske, T. R., Kelly, H. M. Y., Lopez-Nicora, H. D., Lux, L., Malvick, D. K., Mangel, D., Markell, S. G., Mueller, D. S., Scherer, J. M., Sikora, E. J., Price, P. P., Sattler, J., Smith, D. L., Telenko, D. E. P., Webster, R. W. 2025. Predictive modeling and field evaluation for a smarter approach to manage frogeye leaf spot of soybean in the U.S. CANVAS 2025 (Tri-Societies Meeting), Salt Lake City, UT, November 9-12, 2025.

Peer-reviewed manuscript submitted in 2025:
Gonzalez-Acuna, J. F., Allen, T. W., Bish, M. D., Bradley, C. A., Camiletti, B. X., Chilvers, M., Dangal, N. K., Diaz-Arias, M. M., Fakhoury, A. M., Faske, T. R., Gleason, M. L., Hansen, B. C., Kelly, H. M. Y., Lopez-Nicora, H. D., Lux, L., Malvick, D. K., Mangel, D., Markell, S. G., Mueller, D. S., Price, P. P., Renfroe-Becton, H., Scherer, J. M., Sikora, E. J., Smith, D. L., Striegel, A., Tekenko, D. E. P., and Webster, R. W. 2025. Exploring the environment-related risk of frogeye leaf spot (caused by Cercospora sojina) in soybean across U.S. regions through logistic regression and machine learning models. Scientific Reports (submitted).

Reference:
Ciampi-Guillardi, M., Ramiro, J., Duarte de Moraes, M. H., Goldoni Barbieri, M. C., and Massola Jr., N. S. 2020. Plant Disease 104:3002-3009. https://doi.org/10.1094/PDIS-02-20-0231-RE.

View uploaded report

Uniform soybean foliar fungicide field trials were conducted across 22 different field sites, in which thirteen treatments and a nontreated check were evaluated. Primary disease pressure came from frogeye leaf spot (FLS; caused by Cercospora sojina) and Septoria brown spot (SBS; caused by Septoria glycines). Averaged across all locations, all treatments except Oxidate reduced FLS severity compared to the nontreated control, and all treatments except Badger, Affiance, “generic Quilt” (R5), and Oxidate reduced SBS severity compared to the nontreated control. In addition, only plots treated with Affiance (R3), Delaro Complete (R3+R5 and R5 alone), “generic Quilt” (R5), Oxidate, Viatude, Miravis Top (R3+R5 and R5 alone) resulted in a significantly greater yield than the nontreated control. The results from the uniform fungicide trial will be used to help revise the 2026 edition of the Crop Protection Network Soybean Foliar Fungicide Efficacy Guide. In addition, the data from these trials are being used to test, adjust, and optimize disease prediction models

Spore traps were deployed in soybean fields across 19 to 20 states in 2023 and 2024. Quantification of spores of Cercospora species that cause Cercospora leaf blight (CLB) of soybean showed that spores of at least one of the Cercospora species were detected in every state. This suggests that CLB pathogens are widespread across the U.S., and that environmental factors likely are driving incidence and severity of CLB. In addition, differences in which species were detected existed across a field season within states. These results help scientists better understand the epidemiology of the Cercospora leaf blight pathogens, and that information will be used to develop forecasting models.

A frogeye leaf spot risk tool was launched on the Crop Protection Network for the 2025 growing season. This tool has a user-friendly interface where multiple fields (locations) can be added to monitor risk during critical stages (typically between R1 and R5 growth stages). Validation of the frogeye leaf spot risk tool is ongoing, but so far, the model has been accurate in predicting frogeye leaf spot across a large geography. Soybean farmers across the U.S. are now able to utilize this tool to help them make better informed decisions for management of frogeye leaf spot.

It is critically important that disease prediction tools that will help farmers make fungicide application decisions be developed and expanded. Such tools will benefit production and profitability of farms, while also reducing the potential risk of exposing both plant pathogens and human pathogens to fungicides that could lead to the selection of fungicide-resistant strains.