Project Details:

Survey and Baseline Fungicide Sensitivities of Fungal Pathogens in Mid-Atlantic Soybean Production

Parent Project: This is the first year of this project.
Checkoff Organization:Delaware Soybean Board
Categories:Soybean diseases
Organization Project Code:
Project Year:2019
Lead Principal Investigator:Alyssa Koehler (University of Delaware)
Co-Principal Investigators:
Keywords: fungi , plant pathology , soilborne pathogens , Disease, Fungicide, fungicide sensitivity

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

Fungal pathogens can be very damaging to soybean (Glycine max (L.) Merrill) production reducing both yield and quality. Environmental conditions can impact disease severity and favor the development of certain organisms. In the Mid-Atlantic, 2018 was a very wet year with widespread fungal issues that resulted in reduced seed quality as harvests were delayed. This project aims to survey Mid-Atlantic soybean farms to collect soilborne and foliar fungal pathogens. Isolates obtained in this survey that represent dominant pathogen groups will be used for in-vitro fungicide trials to obtain baseline fungicide sensitivities against products with potential as seed treatments or foliar application to manage disease. Through this survey locations with high disease pressure will be identified for future fungicide efficacy trials or other on-farm collaborations.

This survey is intended to complement a proposal submitted to the Maryland Soybean Board to quantify nematode populations and to identify fungal isolates collected in this project to correct species using molecular PCR identification. Certain fungal species can be difficult to separate by morphology alone and molecular tools offer a way to confirm proper identification. Knowing the correct identity of a pathogen can impact management recommendations for variety selection or fungicide program. As isolates are separated by species, in-vitro fungicide trials will provide important data on the response of each species to different fungicides to aid in understanding of fungicide efficacy. This data can then be used to inform future fungicide efficacy field trials.

Approximately 60 farms across DE and MD will be identified for sampling. Half of the sites will be full season and the other half will be double crop soybeans. Weekly scouting for symptomatic plants will be conducted and isolations will be made from root, leaf, or stem tissue as appropriate. While many fungal species will likely be collected in this project, this objective will focus on establishing fungicide baselines for Diaporthe sp., M. phaseolina, and possibly C. kikuchii depending on in-season environmental conditions and isolation frequency. Based on the number of isolates obtained, 20-40 isolated for each organism will be selected to be screened against three to four fungicides with potential for foliar or seed treatment efficacy. Four fungicide concentrations for each fungicide product will be selected to establish EC50 (effective concentration for 50% inhibition of mycelial growth) values. Fields with higher disease pressure will be noted for potential collaborations in future fungicide efficacy research trials for foliar or seed treatment products.

Findings from this project will be shared through the University of Delaware’s Weekly Crop Update ( which reaches over 700 growers, consultants, and stakeholders and provides a platform to discuss disease concerns and other production issues. Data on fungal species observed and baseline fungicide sensitivities will also be shared through training events, fact sheets, and extension presentations.

Project Objectives

1. Characterize fungal pathogens in Mid-Atlantic soybean production and observe the frequency of isolation across farms.
2. Build a collection of isolates that can be screened for fungicide sensitivity and used in other projects to verify pathogen species using molecular protocols.
3. Identify locations with high disease pressure that may be used for future research and demonstration plots.

Project Deliverables

Updates in Weekly Crop Update as diseases are observed, extension presentations, relevant publications and data share through social media platforms

Progress of Work

Updated July 6, 2019:
At this time, survey sites have been identified. Tentative plans are to survey from 10 organic fields and 50 conventional fields. Approximately 35 fields are located in Delaware and 25 in Maryland. Fields include full season and double crop beans, with a higher percentage in double crop production. Disease surveys began last week and all of the farms included in the survey will be visited periodically from July - October to collect diseased samples and build a collection of isolates to analyze using molecular techniques. I plan to visit each farm 1-2 times during the survey period. Isolates that are collected through this summer will be screened for fungicide sensitivities in late fall. This proposal is also supporting the hourly wages of a recently graduated student that will assist with collecting, maintaining, and screening fungal isolates for this project. She plans to enroll in my program as a MS student in Spring 2020.

Final Project Results

Updated March 31, 2020:

View uploaded report PDF file

Soilborne pathogens can reduce soybean yield and quality. Limited research has been conducted in recent years to characterize and identify problematic fungal pathogens to species. Project objectives included: (1) Characterize fungal pathogens in Mid-Atlantic conventional and organic soybean production and observe the frequency of isolation across farms. (2) Build a collection of isolates that can be screened for fungicide sensitivity and used in other projects to verify pathogen species using molecular protocols. (3) Identify locations with high disease pressure that may be used for future research and demonstration plots. In 2019, sixty field sites were surveyed. Soilborne fungal pathogens were isolated from 40% of sampled fields. Three species of the fungus Diaporthe were isolated from stem and root tissue across 17% of fields, along with Macrophomina phaseolina, the causal agent of charcoal rot, isolated from 17% of fields. A subset of twenty-six isolates were selected for in-vitro fungicide efficacy to three fungicides. All fungi screened were sensitive to all products with ED50 values ranging from <0.01 – 2.4 ppm. From this trial, a field was identified that will be used for soybean seed treatment efficacy trials in 2020, other field sites with Diaporthe species present were identified for continued survey work in 2020.

Benefit to Soybean Farmers

Increased understanding of pathogen distribution and species level identification across Delaware to better tailor management strategies.

Performance Metrics

Project Years