Project Details:

Increasing our knowledge of the incidence of insensitivity of Cercospora sojina to SDHI and QoI fungicides in Illinois

Parent Project: This is the first year of this project.
Checkoff Organization:Illinois Soybean Association
Categories:Soybean diseases
Organization Project Code:
Project Year:2021
Lead Principal Investigator:Nathan Kleczewski (University of Illinois at Urbana-Champaign)
Co-Principal Investigators:

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

Project Description:
Frogeye leaf spot (FLS) resistance to strobilurin fungicides has been documented in Southern IL, and many farmers don’t have access to useful information on the distribution of insensitive FLS in Illinois. This work includes a two-year survey for FLS in IL and characterizes the sensitivity profiles of pathogen isolates.

Summary/Project Scope:
Summary of Project

Frogeye leaf spot (FLS) is a potentially yield limiting disease in Illinois, and the most impactful foliar disease encountered in the state. Resistance to QoI (strobilurin) fungicides was documented nearly a decade ago in Southern Illinois. Currently our clientele do not have access to up to date information on the distribution of QoI insensitive FLS in Illinois. In addition, we hypothesize that increased use and exposure to SDHI fungicide active ingredients may be resulting in a buildup of insensitivity within FLS populations, particularly in southern Illinois where the disease is more frequently encountered. Lastly, many producers in the state would like to better understand the relative profitability of managing FLS in the state. In this project we will conduct a two year survey for FLS in Illinois and characterize the sensitivity profiles of isolates recovered to SDHI (group 7) and QoI (group 11) fungicide modes of action. In addition, we will set out multiple small plot trials throughout the state to assess the effectiveness and profitability of variety and fungicide selection for managing FLS in Illinois using established metaanalytical methodology. Data from this project will be used to develop Illinois-specific educational materials on fungicide resistance development and integrated management of FLS, and provide data that could be used to generate profitability tools in the future. It will be the first work we are aware of to assess SDHI sensitivity profiles in C. sojina in the United States. Finally, funds will support the next generation of agricultural researchers, helping to support a student with interest in applied agriculture in pursuing their MSc. degree in crop sciences at UIUC. This is a proposal for year one of a two year project.

Problem Statement

Frogeye leaf spot (FLS), caused by the fungal pathogen Cercospora sojina, is the most yield limiting a foliar disease of soybeans in Illinois. In 2018, an estimated 7,564,944 bushels ($70,955,753 US). The average annual loss due to FLS in Illinois from 2012-2019 is 2,474,909 ($23,953,614 US) [1] . The fungus survives on soybean residue and occasionally can be seed borne. Spores of the fungus are dispersed locally from residue and from within foliar lesions to unaffected soybean foliage and plants. High relative humidity and warm temperatures favor spore production and infection of leaves. Yield losses exceeding 30% can occur following significant reductions in foliar leaf area [2]. In Illinois, FLS historically was only of significance in the southern half of the state. In these areas, repeated use of foliar fungicides in the strobilurin class [quinone outside inhibitor-QoI (Fungicide Resistance Action Committee ‘FRAC’ group 11)] resulted in the development of elevated QoI resistant populations throughout the region. Recently, we have had many conversations with industry, producers, and agronomists about how widespread QoI resistance is within the state, especially in Central and Northern Illinois, where the disease historically has not been yield limiting. The answer is- we don’t know. Currently the only data available is nearly a decade old, and focused on southern regions of the state where the issue started in Illinois

[3-5]. In central and northern Illinois, some producers utilize foliar fungicides containing a QoI mode of action (e.g. Headline, Aproach, Quadris), for “plant health” benefits despite the absence of significant FLS pressure. This practice can inadvertently select more QoI insensitive populations, which results in the loss of efficacy for fungicides with QoI active ingredients over time, and eventually lead to complete failure of the fungicide mode of action to control pathogenic fungal populations.

Once populations are insensitive to a QoI fungicidal active ingredient, they will be cross-resistant to other active ingredients within that chemical group. This means that if a producer applies a QoI to that population, it will not suppress FLS development, and the producer will suffer not only from FLS related losses, but the cost of product and application. A similar issue occurred recently in Iowa, where last season FLS was widespread throughout the state. Where the disease was present at elevated levels, increased numbers of QoI-insensitive individuals occurred. This is a situation we want to avoid in Illinois. A better understanding of the actual distribution of QoI insensitivity issues will help inform soybean producers as to best management practices for effectively managing this disease, including the use of FLS-resistant soybean cultivars and timely applications of fungicides when necessary.

In addition, fungicides belonging to the succinate dehydrogenase inhibitor (SDHI) mode of action are becoming more common in commercial fungicides used in soybean production, and are considered moderate to high risk for development of fungicide insensitivity [6] . Unlike QoI fungicides, industry is only utilizing SDHI active ingredients as part of premix fungicide products containing 2-3 fungicide modes of action. This is due primarily to limited modes of action available for use and in development, as well as a means to extend the lifespan of active ingredients. On first look, this is a way to reduce buildup of fungicide insensitive populations in a typical situation. However, if a fungal population already is insensitive to one of the chemistries in the premix, additional selection pressure will be placed on the remaining active ingredients in the product. This results in the eventual failure of other fungicide active ingredients over time (Figure 1). Such was the case for Didymella bryoniae (gummy stem blight) in cucurbits in Indiana, Georgia, and Florida [7, 8]. In this system, underlying QoI resistance issues were not known, and a premix fungicide containing QoI and SDHI active ingredients was totally ineffective for controlling this disease within three years of its release. Currently the sensitivity profiles of C. sojina to SDHI modes of action in Illinois is unknown. Given that QoI insensitivity has been problematic in southern Illinois for several years now, we should be able to detect insensitivity to SDHI’s if it has developed. SDHI’s are also used in soybean seed treatments (e.g iLeVO), which may impose additional selection pressure on populations of C. sojina in the state. Understanding the potential for SDHI insensitivity to develop in C. sojina will become increasingly important in the future as these active ingredients continue to be released and utilized in soybean production.

Lastly, buildup of insensitive populations of C. sojina can be reduced by utilizing an integrated management plan that includes the use of tillage/rotation, FLS resistant cultivars, and an appropriate fungicide if warranted. A question we often receive is “Do I need to spray a fungicide on my beans” or “What is the likelihood that making a fungicide application for FLS will pay for me?” We can answer these questions through directed, Illinois-centric research conducted across the state, under different environmental conditions and disease pressures. Providing relevant, state-specific measures of the utility and profitability of these practices will help inform and educate the agricultural communities as to how to profitably FLS under Illinois conditions.

Project Objectives

Evidence of need

We have had several conversations with industry and producers over the past two growth seasons pertaining to fungicide insensitivity of FLS in Illinois. Currently we do not have up to date answers for our clientele. Resistance of populations of FLS to QoI modes of action was demonstrated in Illinois over ten years ago. However, no efforts to track populations for fungicide insensitivity, this issue have been developed, demonstrated, and communicated in Illinois. Additional potential issues, such as SDHI insensitivity and profitability of IPM practices for FLS have not been conducted.

1) Collect samples of FLS from throughout Illinois. Determine fungicide sensitivity profiles (QoI and SDHI) of isolates collected.

2)Conduct small plot research with producers throughout Illinois to assess the probability of different IPM strategies for managing FLS.

3)Educate producers on fungicide resistance development and its management in Illinois soybeans and profitable FLS management.

Project Deliverables

Proposed Methods/Tactics
A graduate student will be recruited to lead these projects as part of her MS.C program. The student will work with industry, producer, and extension partners to collect FLS infected soybean tissue from across the state. In addition, fields will be surveyed in underrepresented areas of the state, for example central and Northeast Illinois. Samples will be placed in plastic bags on ice, and shipped to the UIUC pathology lab. Spores of C. sojina will be identified with the aid of a hand lens and single spore isolations carried out onto soybean/lima bean agar [3]. If no spores are present, sporulation will be induced using humidity chambers. Poison plate assays will be used to assess the sensitivity of individual isolates to technical grade pyraclostrobin, azoxystrobin, fluopyram, fluxapyroxad, solatenol, and other new SDHI active ingredients as determined by industry colleagues and availability. The values at which 50% of sporulation and growth is reduced relative to unamended controls will be determined using standard curve fitting procedures

[9-12]. Samples will be collected from at least 25 locations and a minimum of 50 isolates collected from samples. We will focus on fields with severe FLS or fields where fungicide applications have been made but the disease is present as these have a greater likelihood of having elevated fungicide resistant populations.

We will establish 5-8 locations throughout Illinois in 2021 to assess the impacts of cultivar resistance and fungicide on the likelihood for a particular management strategy to pay. Locations will be established on research and grower farms, in fields with a recent history of FLS. Two cultivars (one resistant, one susceptible to FLS) will be planted at each location in small plots, following our standard protocols. Efforts to plant into continuous soybean will be made, as the focus on this work will be fungicide and cultivar interactions. Cultivars will be overlaid with a fungicide treatment targeting FLS. Treatments will include a non treated check, Delaro, Veltyma, Lucento, Miravis Top, Aframe Plus, Domark, and Tilt applied at 15gpa over the inner 5ft of plots using a backpack C02 sprayer equipped with 4, Teejet 80v02 nozzles. All products will be applied with 0.250% NIS. These products represent a mix of newer “premium” products and an older, or generic cheaper fungicides, allowing us to calculate profitability indices over a larger range of price points. Additional fungicides could be added, but at the sacrifice of varieties. Each treatment will be replicated 4 times at each site, resulting in 64 plots per site and 384 plots in the season. In order to generate sufficient data for probability analysis, and to ensure a wide range of environmental conditions to broaden inference, a second year of data will be required.

The percent foliar severity for frogeye leaf spot will be assessed for all plots at V5/6, R3, and R5, and the aeea under the disease progress curve determined [13]. Although FLS will be the focus, other diseases will be rated if present. Yield for each plot will be obtained with a Masset 8xP small plot combine, and yields adjusted for population. Subsamples of seed will be collected and rated for infection by C. sojina, which can infect pods and seeds later in the season. Confirmation for C. sojina as the agent of discoloration will be made by surface sterilizing seeds, isolating fungi in standard media, and sequencing the ITS region of the fungal genome following standard lab protocols [14]. Surveys of industry and producers will be used to establish average application costs for the three fungicides used in this work. These values, as well as yields, will be used to determine the probability of a particular program to produce sufficient yields improvements to pay for product application and deductions due to potential grain quality issues following established metaanalytical methods

[15-17]. In addition, the probability of a given practice reducing FLS to a specified amount will be assessed. Exploration of this dataset will potentially enable us to approximate potential disease thresholds for FLS in Illinois soybeans. However, two seasons of data will be needed to produce sufficient data to conduct these analyses and ensure adequate environmental diversity.

Communication of Impact

Data will be summarized and published at ISA and UIUC outreach venues as described previously. A preliminary profitability calculator could be developed with at least two years of data, which may potentially lend itself to additional work to provide a profitability calculator for soybean foliar fungicides in Illinois in future years. Project information will be provided by the graduate student at university field days. The student will present data at either the North Central APS meeting or APS national meeting in 2022. A webinar on FLS and fungicide resistance in Illinois will be developed and presented through ISA and UIUC, and a factsheet on FLS and fungicide resistance developed. Results will be shared at UIUC Extension certified crop master sessions, industry meetings, the UIUC ag day, and online venues and webinars. Results will be presented by both PI Kleczewski and the MS student, depending on the venue. The student will be responsible for developing all extension materials and conducting all aspects of this work.

Results will be published in peer-reviewed scientific journals and presented at scientific meetings such as APS. ISA will be credited in all publications and presentations.

Lastly, in order to assess knowledge gained and utility of deliverables, pre and post surveys will be conducted when possible at webinars and in person meetings. Data will be shared with ISA. Data will be shared with ISA.


Quarter One activities: Begin planning 2021 field season. Request seed and chemical treatments. Locate collaborators to help identify locations and collect samples.
Quarter Two activities: Plant locations, rate and treat all locations. Start to collect FLS isolates.
Quarter Three activities: Harvest all plots purify all FLS isolates. Begin fungicide sensitivity assays.
Quarter Four activities: analyze all data and provide year one report to ISA and at extension events during winter.

Progress of Work

Final Project Results

Benefit to Soybean Farmers

The proposed research will help maintain productivity and profitability of soybean producers in Illinois. Impacts of FLS and associated financial losses can be reduced by developing and communicating an effective integrated management plan. Profitability of management can be assessed and communicated through relevant, state-level research. Tracking the distribution and source of fungicide insensitivity issues in FLS will help to spread awareness and communicate the need for selecting more appropriate fungicides, utilizing IPM to reduce overall disease presence, and promoting profitable strategies for the use of fungicides. This will not only reduce potential losses in profit, but will help extend the longevity of fungicide active ingredients in the state

Performance Metrics

Target Market/Audience:
Growers, crop consultants, agronomists, and others in the agricultural community.

Output (s):
Indication of the frequency of QoI and SDHI insensitive C. sojina populations across selected fields in Illinois.
Assessment of knowledge gained and usefulness of information

Outcome (s):
Increased understanding of fungicide resistance in Illinois FLS populations
Increased profitability through improved yields and reduced input costs
Improved profitability by reducing the buildup of fungicide resistant FLS within the state

Project Years