Soybean is a major field crop in the North Central region and the entire United States. Soybeans are susceptible to an array of disease-causing microbes that can result in significant costs for the farmer and to the environment, due to the application of pesticides to control them. A major premise of the study of plant pathology is that for diseases of plants to occur there must be the presence of a virulent pathogen, a susceptible host, and an environment that is favorable for disease development (host, pathogen, and environment are the legs of the triangle). This last factor stands to be a major driver of plant disease. In fact, the environment can influence when and where pathogens will cause disease problems and a changing climate can result in the occurrence of new diseases affecting soybeans.

Recent changes in weather conditions have led to the re-emergence of some diseases in the North Central region or the expansion of diseases into the region. For example, frogeye leaf spot (caused by the fungus Cercospora sojina) has been an increasing problem in the upper Midwest. In recent years this pathogen has become a more significant issue, causing severe epidemics in states where it traditionally had not been a problem. It is thought that due to climate change, the fungus can survive warmer winters (Roth et al., 2020). In addition, warmer growing seasons result in wetter growing seasons, meaning wind-dispersed rain, and splashing rain, are prominent for dispersal of the frogeye leaf spot pathogen. High humidity also makes for conducive conditions for disease development and high severity.

Cropping systems also have changed leading to increased continuous soybean production and no-till cropping systems. This leads to larger proportions of pathogen inoculum surviving in soybean fields. These changes in production practices over the past decade combined with challenging weather events, require creative solutions for sustainably managing these diseases.

Seedling Disease Complex. Water molds (> 40 species of Pythium, and Phytophthora sojae, Phytophthora sansomeana), and true fungi (Fusarium spp. (including SDS), Macrophomina phaseolina (charcoal rot), and Rhizoctonia solani) have each alone or in combination contributed to stand loss as well as replanting. Much of the research to date has focused on each of these individually, but based on our isolations and diagnostics, it is clear that an approach that focuses on managing these diseases as a complex throughout the soybean growth cycle from planting to harvest is sorely needed. Performing trials with uniform protocols across states, looking for products (seed treatments) that might balance management of more than one pathogen of seedlings is desired.
Foliar Pathogens and Fungicide Resistance. Frogeye leaf spot, caused by Cercospora sojina, has become re-established and is expanding in the North Central Region, and there is little information on the best fungicide timing, most effective fungicides, or the best way to scout to assess the need for a fungicide application (e.g., by foot, drone, or airplane). Specifically, at each growth stage, what levels of disease contribute to yield loss for each maturity group? Experiments to assess if this fungus overwintered were completed in Ohio and Illinois, but not in regions further north. A predictive tool is needed to determine which years C. sojina will overwinter, the inoculum load in the spring necessary to begin an epidemic, and under what conditions a fungicide spray is warranted.

More importantly, is there a continued shift in this fungal pathogen population towards QoI resistant strains in the North Central Region? Does this shift in fungicide sensitivity indicate a change in winter survival? What is the virulence spectrum of these strains? Are the soybean cultivars and germplasm for this region resistant to these strains? Recent evidence from several team members also suggests that the fungus that causes brown spot is not responding to QoI fungicides as it once did. There are also more reports of subtle shifts towards resistance in some fungi to the triazoles, plus the push by some in industry for half rates of fungicides. The role that this half fungicide rate approach will have on the development of resistance as well as fungicide efficacy in low, moderate, and high disease environments is unknown. Monitoring fungicide sensitivity and recommending appropriate timeliness of fungicide applications are critical for continued successful management.

Stem Diseases and Seed Quality. Northern and southern stem canker, pod and stem blight, brown stem rot, and a various array of other diseases affect seed quality in the North Central Region. The basic pathology and disease cycle of these diseases are largely unknown in the North Central Region. These diseases have long been issues in this region. The distribution of the two stem canker diseases (southern and northern) needs further geographic clarification since resistance varies between these two diseases. Additional immediate and important questions for this complex are: Will southern stem canker replace northern stem canker? Will southern stem canker establish and survive in the soil or on weedy hosts in the region? How often does brown stem rot play a role in the stem disease complex? What resistance levels are readily available to these diseases in the Midwest germplasm? Will fungicides limit or control this complex of organisms? Symptoms of these stem diseases, SDS, stem canker, and brown stem rot are all very similar (especially from roadside truck surveys). Can scouting be improved for accurate sampling and or predictive tools developed for in-field management?

Develop predictive models and model validation. Several soybean disease prediction tools currently exist or are being developed. For example, the Sporecaster prediction tool (Willbur et al., 2018 a and b) was developed for white mold and supported by NCSRP and state-level checkoff funds. Models like this use weather information incorporated into mathematical or statistical models to calculate the risk of disease development and help guide timely fungicide applications. These tools can be adapted and validated for other diseases of concern. Diseases continuing to increase in affecting a large number of acres include frogeye leaf spot and stem canker. The Sporecaster framework is flexible and adaptable to various diseases and the delivery of the tool can be done easily placing the tool in the hands of farmers and consultants.

The impact of new cropping systems on soybean diseases throughout the region. Changes in production systems, seeding rates, cover crops, strip tillage, new bio-active treatments, not to mention sugar, have been incorporated into farmer practices. How and if these practices and products favor or inhibit soybean pathogens is unknown. Fertility and the influence of fertility level on soybean diseases isn’t well understood. Understanding fertility influences on disease will be important for sustainably managing new and emerging diseases into the future.

Overall Goal: To develop improved management strategies, and communication of those strategies, for the sustainable management of the major soybean diseases in the North Central U.S.

Overall Goal: To develop improved management strategies, and communication of those strategies, for the sustainable management of the major soybean diseases in the North Central U.S.

Objective 1: Conduct multi-site-year product efficacy trials to develop a robust, non-partial dataset to educate and inform farmers and practitioners on the performance of disease control products available for soybeans

Objective 1a. Conduct uniform foliar fungicide trials that target a holistic approach to control white mold, frogeye leaf spot, and stem canker (Diaporthe diseases); find programs that might be able to cover these major diseases simultaneously.

Objective 1b. Conduct uniform seed treatment trials to target sudden death syndrome, brown stem rot, Phytophthora root rot, and Pythium root rot.

Objective 2: Conduct research and validation trials to develop and/or validate disease prediction tools or risk studies for major soybean diseases

Objective 2a. Develop a frogeye leaf spot model using the Sporecaster framework.

Objective 2b. Develop prediction tools for stem canker of soybean using the Sporecaster framework.

Objective 2c. Validate an existing soybean sudden death syndrome prediction tool for predicting risk of epidemics in soybean fields.

Objective 3: Develop improved understanding of the biology and epidemiology of emerging and re-emerging diseases of soybean in the North Central Region.

Objective 3a. Monitor for fungicide resistance in the frogeye leaf spot pathogen, Septoria brown spot pathogen, stem canker pathogens, white mold pathogen, Pythium species, and Phytophthora root rot pathogens.

Objective 3b. Develop a better understanding of how to improve seed health and quality with a focus on Diaporthe diseases (stem canker) and brown stem rot.

Objective 3c. Develop improved tools for frogeye leaf spot, sudden death syndrome, and brown stem rot management including fertility impacts on the disease, how rotations influence disease incidence and severity, and how new products like nano-fertilizers and other nanotechnology influence disease.

Objective 3d. Understanding the pathogen complex causing Cercospora leaf blight (CLB) in the North Central region. Conduct a survey in the NC region and understand the pathogen complex and how it relates to what has been identified in the south and mid-south.

Objective 4: Develop extension tools through state extension programs, Crop Protection Network (CPN) and Soybean Research and Information Network (SRIN).

Objective 4a. Use the efficacy information from objective 1a and 1b to inform and update fungicide efficacy charts annually for the Crop Protection Network.

Objective 4b. Communicate with farmers and agribusiness personnel through extension articles, videos, webinars, and field days.

The results of this research will be used to not only increase our understanding of the biology and epidemiology of various diseases on soybean, but will be used to formulate improved, modern, sustainable integrated management decisions for the major diseases of soybean in the North Central Region. Several important outcomes and deliverables will result from this research. These include:
- Companion extension publication detailing the foliar fungicide meta-analysis
- Development of new forecasting tools for frogeye leaf spot and stem canker
- Demonstration plots will be available for field days and other educational opportunities in the participating where integrated strategies for managing the major diseases of the North Central region will be showcased
- Fact sheets and publications will be generated using the most current information as a result of this coordinated effort (many of the personnel on this proposal have extension appointments in addition to their research appointments, and all personnel are well-versed in communicating their research to the public).
- Results of research will be presented at stakeholder meetings
- Blog articles will be written on extension personnel websites
- An electronic book will be developed for Sclerotinia stem rot management

Updated March 24, 2023:
2023 NCSRP Spring Report (March 24, 2023)

Submitted by: Damon L. Smith, University of Wisconsin-Madison

Funding for the second year of this contract work started October 1, 2022. We made excellent progress in the first year of the project (October 2021-September 2022) which was recently reported in the final report submitted January 31, 2023. The research group met on February 28, 2023, after the NCERA 137 (Soybean Diseases) meeting in Pensacola Florida to discuss results from year 1 and to plan for year 2 of our contract work. The meeting lasted two hours and was extremely productive. Brief updates for each objective are below. We are looking forward to continuing our high-impact work on soybean diseases in the North Central region.

Objective 1: Conduct multi-site-year product efficacy trials to develop a robust, non-partial dataset to educate and inform farmers and practitioners on the performance of disease control products available for soybeans.

Objective 1a. Conduct uniform foliar fungicide trials that target a holistic approach to control white mold, frogeye leaf spot, and stem canker (Diaporthe diseases); find programs that might be able to cover these major diseases simultaneously.

The research group will continue into year 2 splitting the foliar uniform fungicide trial (UFT) protocols into two separate protocols. We have generated a general foliar UFT targeted at management of frogeye leafspot, Cercospora leaf blight, and Septoria brown spot. The group finalized this protocol at the February 28th meeting which included 8 core treatments with 3 core inserts for more “northern” locations in the NC region and 2 core inserts for more “southern” locations (ex. Southern Illinois has a different environment than northern Illinois) in the NC region. These data will be combined with 2022 data in a large analysis and the work will be reported in scientific publications as well as in the Crop Protection Network Fungicide Efficacy table updates.

A separate white mold-focused protocol has been generated and finalized (February 28, 2023) for this objective. In 2022, the group felt that white mold necessitated a separate, focused trial to better understand core treatments for management. This protocol includes 12 core treatments and 6 additional optional treatments. The optional treatments mostly focused on drop-nozzle applications and were deemed optional for locations where researchers do not have the equipment to apply those treatments. These data will be combined with those from 2022 in a large analysis and the work will be reported in scientific publications as well as in the Crop Protection Network Fungicide Efficacy table updates.

Objective 1b. Conduct uniform seed treatment trials to target sudden death syndrome, brown stem rot, Phytophthora root rot, and Pythium root rot.

Two uniform seed treatment trials (finalized at the February 28, 2023, meeting) have been generated and will be conducted for this objective. The first protocol focuses on sudden death syndrome and includes 7 seed treatments applied to two varieties (an SDS-susceptible and an SDS-resistant).

As separate uniform fungicide seed treatment trials targeting Pythium and Phytophthora will also be conducted in 2023. As of the February 28, 2023, meeting we were still working with companies to determine final treatments. Our goal will be to include the latest seed treatment products to generate efficacy information to inform our fungicide efficacy tables.

Objective 2: Conduct research and validation trials to develop and/or validate disease prediction tools or risk studies for major soybean diseases.

Modeling work is underway for each specific disease as indicated below.

Objective 2a. Develop a frogeye leaf spot model using the Sporecaster framework.

We now have a graduate student assisting the PI who is aggregating historical datasets of frogeye leafspot data from locations across the NC region. Models are being explored and a beta-testing version of a frogeye leafspot model may be available soon.

Objective 2b. Develop prediction tools for stem canker of soybean using the Sporecaster framework.

Like objective 2a, we are aggregating existing stem canker data to determine the best approach to model stem canker diseases. While the datasets for this disease are not as dense as those for frogeye, we do believe that preliminary models can be generated, and we can leverage the UFT trials in objective 1a to validate these models in future years.

Objective 2c. Validate an existing soybean sudden death syndrome prediction tool for predicting risk of epidemics in soybean fields.

At Michigan State University the MSU SDS risk prediction tool is continuing to be validated (see January 2023 report). Again in 2023 we will collect soil sample data from the SDS UFT seed treatment trials to use as validation data. These data will be combined with 2022 data in a large analysis.

Objective 3: Develop improved understanding of the biology and epidemiology of emerging and re-emerging diseases of soybean in the North Central Region.

An extensive report for this objective, from the year 1 studies, was included in the January 2023 report. Brief updates for year-2 work are included below.

Objective 3a. Monitor for fungicide resistance in the frogeye leaf spot pathogen, Septoria brown spot pathogen, stem canker pathogens, white mold pathogen, Pythium species, and Phytophthora root rot pathogens.

An extensive number of isolates within each pathogen species causing the respective diseases above, have been collected prior to the implementation of this research contract. We are actively documenting and cataloging these isolates, developing protocols, and identifying specific laboratories who can develop baseline fungicide resistance levels in existing isolates. This work is ongoing with interesting results reported in January 2023. This work will continue to monitor fungicide resistance in year-2 of this project.

Objective 3b. Develop a better understanding of how to improve seed health and quality with a focus on Diaporthe diseases (stem canker) and brown stem rot.

A protocol was developed in 2022 to collect seed from multiple fields in states participating in this research contract. The protocol underwent a re-write at the February 28, 2023, meeting to improve our ability to obtain samples. That protocol will be implemented in year-2 of this project.

Objective 3c. Develop improved tools for frogeye leaf spot, sudden death syndrome, and brown stem rot management including fertility impacts on the disease, how rotations influence disease incidence and severity, and how new products like nano-fertilizers and other nanotechnology influence disease.

Two separate uniform research protocols have been generated for this objective. One protocol focuses on sudden death syndrome and includes 6 treatments focused on understanding the interactions of ILEVO seed treatment with traditional soil-applied fertilizers and new foliar-applied fertilizers, on SDS severity. This trial was first implemented across locations in 2022 and will be repeated in 2023.

The second protocol focuses on white mold and includes 6 treatments focused on understanding the interactions of foliar applied fungicide (Endura) and traditional soil-applied fertilizers and new foliar-applied fertilizers on white mold severity. This trial was first implemented across locations in 2022 and will be repeated in 2023.

Objective 3d. Understanding the pathogen complex causing Cercospora leaf blight (CLB) in the North Central region. Conduct a survey in the NC region and understand the pathogen complex and how it relates to what has been identified in the south and mid-south.

Leaf samples will again be collected in 2023. Analysis is ongoing identifying species from the 2022 samples. All data from 2022 and 2023 will be combined for analyses. These analyses should shed light on the Cercospora species present in the North Central region and help guide us on how to better manage these pathogens in soybean.

Objective 4: Develop extension tools through state extension programs, Crop Protection Network (CPN) and Soybean Research and Information Network (SRIN).

Please see specific sub-objectives below for updates.

Objective 4a. Use the efficacy information from objective 1a and 1b to inform and update fungicide efficacy charts annually for the Crop Protection Network.

New updated version of the Foliar Fungicide Efficacy Table for Soybeans and the Seed Treatment Efficacy Table for Soybeans have been released and include data from our year-1 contract work. Those tables can be found here: https://cropprotectionnetwork.s3.amazonaws.com/cpn1019_fungicideefficacycontrolsoybean_2023_draft1-(1).pdf and here: https://cropprotectionnetwork.s3.amazonaws.com/cpn1020_fungicideefficacysoybeanseedling_2023_draft1-(1).pdf. Data from 2023 will be incorporated in future versions of these reports.

Objective 4b. Communicate with farmers and agribusiness personnel through extension articles, videos, webinars, and field days.

As reported in January 2023, we have also generated several new peer-reviewed outreach products during this contract period. The first is a white mold web book. This web book was partially supported by prior NCSRP funding. The funding from this new research contract allowed us to finish up this large project. The web book has been peer-reviewed and is now live, with free access. It can be found here: https://cropprotectionnetwork.org/web-books/white-mold-of-soybean.

A research update titled “Modern Integrated Management Practices for Controlling White Mold of Soybean” was also generated during this period. This research update is based on work funded from a previous proposal on white mold that was funded by the NCSRP. This research update combines information from research and new efficacy data from white mold UFT trials into a concise document outlining modern white mold management recommendations. This research report can be found here: https://cropprotectionnetwork.org/publications/modern-integrated-management-practices-for-controlling-white-mold-of-soybean.

Updated January 25, 2024:
2023 NCSRP Final Report (January 31, 2024)

Submitted by: Damon L. Smith, University of Wisconsin-Madison

The second year of funding for this project started October 1, 2022. We made excellent progress again in the second year of the project and greatly appreciate the support to continue the project into the final year (year 3), expanding and further developing on the progress found below. We have a year-3 planning meeting scheduled for March 5, 2024, which will take place in conjunction with the NCERA 137 meetings in Pensacola Florida. This meeting will be used to finalize protocols and talk through current data. Below please find specific updates on our current progress for each objective of the research contract.

Objective 1: Conduct multi-site-year product efficacy trials to develop a robust, non-partial dataset to educate and inform farmers and practitioners on the performance of disease control products available for soybeans.

Objective 1a. Conduct uniform foliar fungicide trials that target a holistic approach to control white mold, frogeye leaf spot, and stem canker (Diaporthe diseases); find programs that might be able to cover these major diseases simultaneously.

In the first year the research group decided to split foliar uniform fungicide trial (UFT) protocols into two separate protocols. We continued this in year 2 and repeated the general foliar UFT targeted at management of frogeye leafspot, Cercospora leaf blight, and Septoria brown spot. The group finalized this protocol at the March 23, 2022, meeting which included 8 core treatments with 3 core inserts for more “northern” locations in the NC region and 2 core inserts for more “southern” locations (ex. Southern Illinois has a different environment than northern Illinois) in the NC region. Iowa, North Dakota, Indiana, Nebraska, Michigan, Missouri, and Wisconsin participated in year 2 of these trials in 2023. These data are currently being analyzed and combined with year 1. Decisions on year 3 are being made on treatments to include for the third season but may not deviate significantly from previous years to ensure more site-years of data on these programs.

A separate white mold-focused protocol has been generated and finalized (March 23, 2022) for this objective. The group felt that white mold necessitated a separate, focused trial to better understand core treatments for management. This protocol includes 12 core treatments and 5 additional optional treatments. The optional treatments mostly focused on drop-nozzle applications and were deemed optional for locations where researchers do not have the equipment to apply those treatments. In 2023 we repeated this protocol to generate more site-years of data. These data are now being combined with year 1 and additional datasets going back to 2019 to conduct a meta-analysis of fungicide performance on more modern fungicide programs. In 2023 Iowa, Indiana, Michigan, North Dakota, and Wisconsin participated in these trials. Planning is underway for treatments to be evaluated in 2024.

Information from both protocols were used to inform and update efficacy rating for the Soybean Foliar Fungicide Tables for 2024 (see Objective 4a below).

Objective 1b. Conduct uniform seed treatment trials to target sudden death syndrome, brown stem rot, Phytophthora root rot, and Pythium root rot.

Two uniform seed treatment trials (finalized at the March 23, 2022, meeting) have been generated and were conducted for this objective. In 2023 we repeated these studies to compile more site-years of data. The first protocol focuses on sudden death syndrome and includes 7 seed treatments applied to two varieties (an SDS-susceptible and an SDS-resistant). The data are currently being compiled for years 1 and 2 and will be analyzed. A research paper will be written along with an extension fact sheet. This work follows up on previous NCSRP-funded work evaluating seed treatments on varieties with differing resistance. We included the well documented ILEVO and Saltro seed treatments here but have expanded to include several new seed treatments being marketed for SDS management, but have not been evaluated in university trials previously.

Uniform fungicide seed treatment trials targeting Pythium and Phytophthora were performed in Michigan, Wisconsin, Indiana, Iowa in 2023. The field trial in each state consisted of 5 commercially available fungicide seed treatment options (non-treated, Intego Suite, Zeltera Suite, Cruiser Maxx Vibrance, Acceleron) specific for the management of oomycete pathogens like Phytophthora and Pythium. Like the foliar trials, these was a repeat protocol from 2022 to generate more site-years of data. The uniformity of the trial allows us to combine data across all states and make regional conclusions based on pooled data, which is currently underway. In 2024, these trials will be repeated to obtain additional site-years so that a multi-location analysis can be conducted.

Objective 2: Conduct research and validation trials to develop and/or validate disease prediction tools or risk studies for major soybean diseases.

Modeling work is underway for each specific disease as indicated below.

Objective 2a. Develop a frogeye leaf spot model using the Sporecaster framework.

We have done the first round of model development from a multi-site-year dataset of frogeye data. A portion of this data was leveraged against data obtained from the fungicide UFT trials referred to above. Some of the data was historical going back to 2009. We were also able to leverage NCSRP funding against and SSRP multi-regional grant with Dr. Carl Bradley, to augment NCSRP frogeye data with data from southern states. This joint effort has led to the beta version of Frogspotter which will be tested in the field in 2024 in the North Central Region.

Objective 2b. Develop prediction tools for stem canker of soybean using the Sporecaster framework.
We are aggregating existing stem canker data to determine the best approach to model stem canker diseases. While the datasets for this disease are not as dense as those for frogeye, we do believe that preliminary models can be generated, and we can leverage the UFT trials in objective 1a to validate these models in future years.

Objective 2c. Validate an existing soybean sudden death syndrome prediction tool for predicting risk of epidemics in soybean fields.

At Michigan State University the MSU SDS risk prediction tool is being validated through the testing of soil samples collected from 2020 (n=542), 2021 (n=251), and 2022 (n=84). COVID-19 restrictions slowed initial progress on the project. However, the real-time PCR assay has been optimized for detection of Fusarium virguliforme (Fv) in soil samples with a sensitivity of 100 fg of Fv DNA which is approximately 100 spores per half-gram of soil.

Objective 3: Develop improved understanding of the biology and epidemiology of emerging and re-emerging diseases of soybean in the North Central Region.

Please see specific updates for each sub-objective below.

Objective 3a. Monitor for fungicide resistance in the frogeye leaf spot pathogen, Septoria brown spot pathogen, stem canker pathogens, white mold pathogen, Pythium species, and Phytophthora root rot pathogens.

An extensive number of isolates within each pathogen species causing the respective diseases above, have been collected prior to the implementation of this research contract. We are actively documenting and cataloging these isolates, developing protocols, and identifying specific laboratories who can develop baseline fungicide resistance levels in existing isolates. Current progress is detailed below:

At Michigan State University F. virguliforme fungicide sensitivity monitoring has so far screened 75 historical (2009 to 2014) isolates and 79 contemporary (2020-2022) isolates. To date no change in fungicide sensitivity has been observed between historical (Mean EC50 = 2.08 mg/L) and contemporary (Mean EC50 = 1.89 mg/L) isolates. Efforts are currently focused at adding additional states and isolates.

The in vitro sensitivity of isolates of D. caulivora and D. longicolla to Difenaconazole (DMI) fungicide was determined. Twelve isolates of D. longicolla [Alabama (1), Minnesota (1), Nebraska (1), Mississippi (1), South Dakota (2), Michigan (2), Indiana (4),] and five isolates of D. caulivora [Wisconsin (1), New York (1), Delaware (1), Michigan (1), South Dakota (1)] from soybean between 2014 and 2017 were evaluated. The technical grade formulation of difenaconazole (95% a.i.; Syngenta Crop Protection, NC) was dissolved in acetone to obtain a stock solution of 100 mg/ml. Fungicide sensitivity was determined by the radial mycelial growth on 2% water agar amended with 0, 0.01,0.02, 0.04, 0.2, 1, 5, and 20.0 µg/ml difenaconazole. The experiment was conducted twice in a completely randomized design and each of the Diaporthe isolates was inoculated with a 6-mm-diameter mycelial plug onto three replicate plates of different fungicide concentrations. Plates were incubated for five days at 22°C in the dark before the radial growth was measured. Significant differences in EC50 values were observed among the isolates of D. caulivora (0.032 to 0.303 µg ml-1; p <0.0001) and D. longicolla (0.012 to 1.478 µg ml-1; p = 0.032) indicating that the isolates of D. caulivora and D. longicolla may differ in their sensitivity to Difenaconazole (DMI) fungicide.

In Ohio, Research in this objective was focused on the white mold pathogen (Sclerotinia sclerotiorum), the stem canker pathogens (Diaporthe spp.), and the SDS pathogens (F. virguliforme) during 2022. Fluopyram is a common active ingredient in fungicides advertised to manage white mold (ex: Delaro Complete). The activity of fluopyram on Sclerotinia sclerotiorum growth was tested on 74 isolates collected from two time ranges: pre-2000 and post-2014. In total, 74 Sclerotinia sclerotiorum isolates were tested for sensitivity to fluopyram. Overall, there was no significant difference in fluopyram tolerance between the two populations of Sclerotinia sclerotiorum isolates. This suggests that fluopyram still has good efficacy in managing this disease, though timing of the application remains critical for optimal control. Further, screening 79 F. virguliforme isolates from 9 North-Central states against fluopyram further demonstrates that this fungicide still has good efficacy in managing this pathogen too. Finally, 35 isolates of Diaporthe spp. were screened for sensitivity to the QoI fungicide azoxystrobin. There is strong evidence to suggest that specific species within the Diaporthe genus respond differently to azoxystrobin, emphasizing the importance of getting an accurate diagnosis of what species is present in problematic fields with histories of stem canker. Individual isolates of all pathogens demonstrate some tolerance to each chemistry, and research in 2023 looked at the genetics of each pathogen to identify mutations that might confer fungicide resistance.

Objective 3b. Develop a better understanding of how to improve seed health and quality with a focus on Diaporthe diseases (stem canker) and brown stem rot.

A protocol was developed in 2022 to collect seed from multiple fields in states participating in this research contract. This protocol will be implemented at harvest in years with clear disease issues, to understand the impact that Diaporthe diseases and brown stem rot have on seed quality. In 2022 and 2023, no visible issues were identified, thus the protocol was not evaluated. We will try again in 2024, in hopes we will have locations with visible disease.

Objective 3c. Develop improved tools for frogeye leaf spot, sudden death syndrome, and brown stem rot management including fertility impacts on the disease, how rotations influence disease incidence and severity, and how new products like nano-fertilizers and other nanotechnology influence disease.

Two separate uniform research protocols have been generated for this objective. One protocol focuses on sudden death syndrome and includes 6 treatments focused on understanding the interactions of ILEVO seed treatment with traditional soil-applied fertilizers and new foliar-applied fertilizers, on SDS severity. This trial was first implemented across locations in 2022.

The second protocol focuses on white mold and includes 6 treatments focused on understanding the interactions of foliar applied fungicide (Endura) and traditional soil-applied fertilizers and new foliar-applied fertilizers on white mold severity. This trial was first implemented across locations in 2022.

Data from both trial protocols were obtained. We plan to repeat these studies in 2024 to gain more site-years of data so we can determine which treatments are consistent across location and environments. We hope that we will have reportable data sufficient for a peer-reviewed publication from these trials after the second season.

Objective 3d. Understanding the pathogen complex causing Cercospora leaf blight (CLB) in the North Central region. Conduct a survey in the NC region and understand the pathogen complex and how it relates to what has been identified in the south and mid-south.

Leaf samples will again be collected in 2024. Analysis is ongoing identifying species from the 2022 and 2023 samples. All data from 2022 and 2023 will be combined for analyses. These analyses should shed light on the Cercospora species present in the North Central region and help guide us on how to better manage these pathogens in soybean.

Objective 4: Develop extension tools through state extension programs, Crop Protection Network (CPN) and Soybean Research and Information Network (SRIN).

Please see specific sub-objectives below for updates.

Objective 4a. Use the efficacy information from objective 1a and 1b to inform and update fungicide efficacy charts annually for the Crop Protection Network.

New updated version of the Foliar Fungicide Efficacy Table for Soybeans and the Seed Treatment Efficacy Table for Soybeans have reviewed incorporating data from above objectives. These will be posted soon for the 2024 season and will be available on the Crop Protection Network Website: https://cropprotectionnetwork.org.

Future versions of these tables will continue to be updated with the information generated from Objectives 1a and b of this research contract.

Objective 4b. Communicate with farmers and agribusiness personnel through extension articles, videos, webinars, and field days.

A research update titled “Creation of New Soybean Varieties with High Levels of Resistance to White Mold” was also generated during this period. This research update is based on work funded from a previous proposal on white mold that was funded by the NCSRP. This research update presents results and development of 4 soybean lines that are highly resistant to white mold: https://cropprotectionnetwork.org/publications/creation-of-new-soybean-varieties-with-high-levels-of-resistance-to-white-mold.

2023 NCSRP Final Report (January 31, 2024)

Submitted by: Damon L. Smith, University of Wisconsin-Madison

The second year of funding for this project started October 1, 2022. We made excellent progress again in the second year of the project and greatly appreciate the support to continue the project into the final year (year 3), expanding and further developing on the progress found below. We have a year-3 planning meeting scheduled for March 5, 2024, which will take place in conjunction with the NCERA 137 meetings in Pensacola Florida. This meeting will be used to finalize protocols and talk through current data. Below please find specific updates on our current progress for each objective of the research contract.

Objective 1: Conduct multi-site-year product efficacy trials to develop a robust, non-partial dataset to educate and inform farmers and practitioners on the performance of disease control products available for soybeans.

Objective 1a. Conduct uniform foliar fungicide trials that target a holistic approach to control white mold, frogeye leaf spot, and stem canker (Diaporthe diseases); find programs that might be able to cover these major diseases simultaneously.

In the first year the research group decided to split foliar uniform fungicide trial (UFT) protocols into two separate protocols. We continued this in year 2 and repeated the general foliar UFT targeted at management of frogeye leafspot, Cercospora leaf blight, and Septoria brown spot. The group finalized this protocol at the March 23, 2022, meeting which included 8 core treatments with 3 core inserts for more “northern” locations in the NC region and 2 core inserts for more “southern” locations (ex. Southern Illinois has a different environment than northern Illinois) in the NC region. Iowa, North Dakota, Indiana, Nebraska, Michigan, Missouri, and Wisconsin participated in year 2 of these trials in 2023. These data are currently being analyzed and combined with year 1. Decisions on year 3 are being made on treatments to include for the third season but may not deviate significantly from previous years to ensure more site-years of data on these programs.

A separate white mold-focused protocol has been generated and finalized (March 23, 2022) for this objective. The group felt that white mold necessitated a separate, focused trial to better understand core treatments for management. This protocol includes 12 core treatments and 5 additional optional treatments. The optional treatments mostly focused on drop-nozzle applications and were deemed optional for locations where researchers do not have the equipment to apply those treatments. In 2023 we repeated this protocol to generate more site-years of data. These data are now being combined with year 1 and additional datasets going back to 2019 to conduct a meta-analysis of fungicide performance on more modern fungicide programs. In 2023 Iowa, Indiana, Michigan, North Dakota, and Wisconsin participated in these trials. Planning is underway for treatments to be evaluated in 2024.

Information from both protocols were used to inform and update efficacy rating for the Soybean Foliar Fungicide Tables for 2024 (see Objective 4a below).

Objective 1b. Conduct uniform seed treatment trials to target sudden death syndrome, brown stem rot, Phytophthora root rot, and Pythium root rot.

Two uniform seed treatment trials (finalized at the March 23, 2022, meeting) have been generated and were conducted for this objective. In 2023 we repeated these studies to compile more site-years of data. The first protocol focuses on sudden death syndrome and includes 7 seed treatments applied to two varieties (an SDS-susceptible and an SDS-resistant). The data are currently being compiled for years 1 and 2 and will be analyzed. A research paper will be written along with an extension fact sheet. This work follows up on previous NCSRP-funded work evaluating seed treatments on varieties with differing resistance. We included the well documented ILEVO and Saltro seed treatments here but have expanded to include several new seed treatments being marketed for SDS management, but have not been evaluated in university trials previously.

Uniform fungicide seed treatment trials targeting Pythium and Phytophthora were performed in Michigan, Wisconsin, Indiana, Iowa in 2023. The field trial in each state consisted of 5 commercially available fungicide seed treatment options (non-treated, Intego Suite, Zeltera Suite, Cruiser Maxx Vibrance, Acceleron) specific for the management of oomycete pathogens like Phytophthora and Pythium. Like the foliar trials, these was a repeat protocol from 2022 to generate more site-years of data. The uniformity of the trial allows us to combine data across all states and make regional conclusions based on pooled data, which is currently underway. In 2024, these trials will be repeated to obtain additional site-years so that a multi-location analysis can be conducted.

Objective 2: Conduct research and validation trials to develop and/or validate disease prediction tools or risk studies for major soybean diseases.

Modeling work is underway for each specific disease as indicated below.

Objective 2a. Develop a frogeye leaf spot model using the Sporecaster framework.

We have done the first round of model development from a multi-site-year dataset of frogeye data. A portion of this data was leveraged against data obtained from the fungicide UFT trials referred to above. Some of the data was historical going back to 2009. We were also able to leverage NCSRP funding against and SSRP multi-regional grant with Dr. Carl Bradley, to augment NCSRP frogeye data with data from southern states. This joint effort has led to the beta version of Frogspotter which will be tested in the field in 2024 in the North Central Region.

Objective 2b. Develop prediction tools for stem canker of soybean using the Sporecaster framework.
We are aggregating existing stem canker data to determine the best approach to model stem canker diseases. While the datasets for this disease are not as dense as those for frogeye, we do believe that preliminary models can be generated, and we can leverage the UFT trials in objective 1a to validate these models in future years.

Objective 2c. Validate an existing soybean sudden death syndrome prediction tool for predicting risk of epidemics in soybean fields.

At Michigan State University the MSU SDS risk prediction tool is being validated through the testing of soil samples collected from 2020 (n=542), 2021 (n=251), and 2022 (n=84). COVID-19 restrictions slowed initial progress on the project. However, the real-time PCR assay has been optimized for detection of Fusarium virguliforme (Fv) in soil samples with a sensitivity of 100 fg of Fv DNA which is approximately 100 spores per half-gram of soil.

Objective 3: Develop improved understanding of the biology and epidemiology of emerging and re-emerging diseases of soybean in the North Central Region.

Please see specific updates for each sub-objective below.

Objective 3a. Monitor for fungicide resistance in the frogeye leaf spot pathogen, Septoria brown spot pathogen, stem canker pathogens, white mold pathogen, Pythium species, and Phytophthora root rot pathogens.

An extensive number of isolates within each pathogen species causing the respective diseases above, have been collected prior to the implementation of this research contract. We are actively documenting and cataloging these isolates, developing protocols, and identifying specific laboratories who can develop baseline fungicide resistance levels in existing isolates. Current progress is detailed below:

At Michigan State University F. virguliforme fungicide sensitivity monitoring has so far screened 75 historical (2009 to 2014) isolates and 79 contemporary (2020-2022) isolates. To date no change in fungicide sensitivity has been observed between historical (Mean EC50 = 2.08 mg/L) and contemporary (Mean EC50 = 1.89 mg/L) isolates. Efforts are currently focused at adding additional states and isolates.

The in vitro sensitivity of isolates of D. caulivora and D. longicolla to Difenaconazole (DMI) fungicide was determined. Twelve isolates of D. longicolla [Alabama (1), Minnesota (1), Nebraska (1), Mississippi (1), South Dakota (2), Michigan (2), Indiana (4),] and five isolates of D. caulivora [Wisconsin (1), New York (1), Delaware (1), Michigan (1), South Dakota (1)] from soybean between 2014 and 2017 were evaluated. The technical grade formulation of difenaconazole (95% a.i.; Syngenta Crop Protection, NC) was dissolved in acetone to obtain a stock solution of 100 mg/ml. Fungicide sensitivity was determined by the radial mycelial growth on 2% water agar amended with 0, 0.01,0.02, 0.04, 0.2, 1, 5, and 20.0 µg/ml difenaconazole. The experiment was conducted twice in a completely randomized design and each of the Diaporthe isolates was inoculated with a 6-mm-diameter mycelial plug onto three replicate plates of different fungicide concentrations. Plates were incubated for five days at 22°C in the dark before the radial growth was measured. Significant differences in EC50 values were observed among the isolates of D. caulivora (0.032 to 0.303 µg ml-1; p <0.0001) and D. longicolla (0.012 to 1.478 µg ml-1; p = 0.032) indicating that the isolates of D. caulivora and D. longicolla may differ in their sensitivity to Difenaconazole (DMI) fungicide.

In Ohio, Research in this objective was focused on the white mold pathogen (Sclerotinia sclerotiorum), the stem canker pathogens (Diaporthe spp.), and the SDS pathogens (F. virguliforme) during 2022. Fluopyram is a common active ingredient in fungicides advertised to manage white mold (ex: Delaro Complete). The activity of fluopyram on Sclerotinia sclerotiorum growth was tested on 74 isolates collected from two time ranges: pre-2000 and post-2014. In total, 74 Sclerotinia sclerotiorum isolates were tested for sensitivity to fluopyram. Overall, there was no significant difference in fluopyram tolerance between the two populations of Sclerotinia sclerotiorum isolates. This suggests that fluopyram still has good efficacy in managing this disease, though timing of the application remains critical for optimal control. Further, screening 79 F. virguliforme isolates from 9 North-Central states against fluopyram further demonstrates that this fungicide still has good efficacy in managing this pathogen too. Finally, 35 isolates of Diaporthe spp. were screened for sensitivity to the QoI fungicide azoxystrobin. There is strong evidence to suggest that specific species within the Diaporthe genus respond differently to azoxystrobin, emphasizing the importance of getting an accurate diagnosis of what species is present in problematic fields with histories of stem canker. Individual isolates of all pathogens demonstrate some tolerance to each chemistry, and research in 2023 looked at the genetics of each pathogen to identify mutations that might confer fungicide resistance.

Objective 3b. Develop a better understanding of how to improve seed health and quality with a focus on Diaporthe diseases (stem canker) and brown stem rot.

A protocol was developed in 2022 to collect seed from multiple fields in states participating in this research contract. This protocol will be implemented at harvest in years with clear disease issues, to understand the impact that Diaporthe diseases and brown stem rot have on seed quality. In 2022 and 2023, no visible issues were identified, thus the protocol was not evaluated. We will try again in 2024, in hopes we will have locations with visible disease.

Objective 3c. Develop improved tools for frogeye leaf spot, sudden death syndrome, and brown stem rot management including fertility impacts on the disease, how rotations influence disease incidence and severity, and how new products like nano-fertilizers and other nanotechnology influence disease.

Two separate uniform research protocols have been generated for this objective. One protocol focuses on sudden death syndrome and includes 6 treatments focused on understanding the interactions of ILEVO seed treatment with traditional soil-applied fertilizers and new foliar-applied fertilizers, on SDS severity. This trial was first implemented across locations in 2022.

The second protocol focuses on white mold and includes 6 treatments focused on understanding the interactions of foliar applied fungicide (Endura) and traditional soil-applied fertilizers and new foliar-applied fertilizers on white mold severity. This trial was first implemented across locations in 2022.

Data from both trial protocols were obtained. We plan to repeat these studies in 2024 to gain more site-years of data so we can determine which treatments are consistent across location and environments. We hope that we will have reportable data sufficient for a peer-reviewed publication from these trials after the second season.

Objective 3d. Understanding the pathogen complex causing Cercospora leaf blight (CLB) in the North Central region. Conduct a survey in the NC region and understand the pathogen complex and how it relates to what has been identified in the south and mid-south.

Leaf samples will again be collected in 2024. Analysis is ongoing identifying species from the 2022 and 2023 samples. All data from 2022 and 2023 will be combined for analyses. These analyses should shed light on the Cercospora species present in the North Central region and help guide us on how to better manage these pathogens in soybean.

Objective 4: Develop extension tools through state extension programs, Crop Protection Network (CPN) and Soybean Research and Information Network (SRIN).

Please see specific sub-objectives below for updates.

Objective 4a. Use the efficacy information from objective 1a and 1b to inform and update fungicide efficacy charts annually for the Crop Protection Network.

New updated version of the Foliar Fungicide Efficacy Table for Soybeans and the Seed Treatment Efficacy Table for Soybeans have reviewed incorporating data from above objectives. These will be posted soon for the 2024 season and will be available on the Crop Protection Network Website: https://cropprotectionnetwork.org.

Future versions of these tables will continue to be updated with the information generated from Objectives 1a and b of this research contract.

Objective 4b. Communicate with farmers and agribusiness personnel through extension articles, videos, webinars, and field days.

A research update titled “Creation of New Soybean Varieties with High Levels of Resistance to White Mold” was also generated during this period. This research update is based on work funded from a previous proposal on white mold that was funded by the NCSRP. This research update presents results and development of 4 soybean lines that are highly resistant to white mold: https://cropprotectionnetwork.org/publications/creation-of-new-soybean-varieties-with-high-levels-of-resistance-to-white-mold.

Soybean farmers and agriculture scientists will benefit from this research by:
-Gaining an improved understanding of key, modern management strategies for diseases of soybean
-Improved management of soybean diseases resulting in improved yield and profitability
-Improved timing of necessary fungicide applications through use of the advisory tool will improve fungicide efficacy and disease control
-Reduced unnecessary fungicide inputs can be avoided
-A better understand of the breadth of fungicide resistance in soybean pathogen populations
-New and improved outreach materials will be developed, including updated web pages and handouts
-An electronic book will be developed to bring a quick, modern, usable reference into the hands of the next generation of farmers and scientists