Updated March 3, 2020:
A manuscript entitled “Multi-location evaluation of fluopyram seed treatment and cultivar on root infection by Fusarium virguliforme, foliar symptom development, and yield of soybean” is in press in Canadian Journal of Plant Pathology (https://doi.org/10.1080/07060661.2019.1666166). The main objective of this study was to evaluate the influence of soybean cultivar and two rates of fluopyram seed treatment on root rot and foliar symptoms of SDS, root weight, grain yield and colonization of roots by F. virguliforme under multiple field conditions. Three seed treatments: (1) base seed treatment (control), (2) base treatment + standard rate of fluopyram (0.15 mg a.i/seed, and (3) base treatment + reduced rate of fluopyram (0.075 mg a.i/seed) were included. Our results showed that both rates of fluopyram significantly reduced root rot and foliar SDS disease severity and increased yield compared to the base treatment. The two rates of fluopyram did not differ in the reduction of root rot or foliar disease severity, but yield was greater with the higher rate than the lower rate in both years. Yield was negatively correlated with root rot at the R4/R5 stage and with foliar disease index. A yield benefit to fluopyram was also observed in a location where only root rot symptoms but no foliar symptoms were observed. These findings suggest that fluopyram seed treatment can reduce the root rot and the foliar phase of SDS, and both phases play an important role in SDS development and yield and should be managed accordingly.

A manuscript titled “Predicting soybean yield and sudden death syndrome development using at-planting risk factors” is in press in Plant Disease (https://apsjournals.apsnet.org/doi/10.1094/PHYTO-02-19-0040-R). The aim of this study was to develop models to predict SDS severity and soybean yield loss using at-planting risk factors to integrate with current SDS management strategies. In 2014 and 2015, field studies were conducted in adjacent fields in Decatur, MI, which were intensively monitored for F. virguliforme and nematode quantities at-planting, plant health throughout the growing season, end-of-season SDS severity, and yield using an unbiased grid sampling scheme. In both years, F. virguliforme and soybean cyst nematode (SCN) quantities were unevenly distributed throughout the field. The distribution of F. virguliforme at-planting had a significant correlation with end-of-season SDS severity in 2015, and a significant correlation to yield in 2014. SCN distributions at-planting were significantly correlated with end-of-season SDS severity and yield in 2015. Prediction models developed through multiple linear regression showed that F. virguliforme abundance (P < 0.001), SCN egg quantity (P < 0.001), and growing season (P < 0.01) explained the most variation in end-of-season SDS (R2 = 0.32), whereas end-of-season SDS (P < 0.001) and end-of-season root dry weight (P < 0.001) explained the most variation in soybean yield (R2 = 0.53). Further, multivariate analyses support a synergistic relationship between F. virguliforme and SCN, enhancing the severity of foliar SDS. These models indicate that it is possible to predict patches of SDS severity using at-planting risk factors. Verifying these models and incorporating additional data types may help improve SDS management and forecast soybean markets in response to SDS threats.

A manuscript titled "Effect of seed treatment and foliar crop protection products on sudden death syndrome and yield of soybean” has been published in Plant Disease (Plant Dis. 103:1712-1720 ). Briefly, in this manuscript seed treatment fungicides, ILeVO and Mertect; seed treatment biochemical pesticides, Procidic and HeadsUp; foliar fungicides, Fortix; and an herbicide, Cobra were evaluated in Illinois, Indiana, Iowa, Michigan, South Dakota, Wisconsin, and Ontario for SDS management in 2015 and 2016. Overall, fluopyram provided the highest level of control of root rot and foliar symptoms of SDS among all the treatments. Foliar application of lactofen reduced foliar symptoms in some cases but produced the lowest yield. In 2015, fluopyram reduced the foliar disease index (FDX) by over 50% in both cultivars and provided 8.9% yield benefit in susceptible cultivars and 3.5% yield benefit in resistant cultivars compared to the base seed treatment (control). In 2016, fluopyram reduced FDX in both cultivars by over 40% compared to the base seed treatment. For yield in 2016, treatment effect was not significant in the susceptible cultivar while in the resistant cultivar, fluopyram provided 3.5% greater yield than the base seed treatment. In this study, planting resistant cultivars and using fluopyram seed treatment were the most effective tools for SDS management. All other products did not affect SDS or inconsistently affected SDS and yield. Although, plant resistance provided an overall better yield-advantage than using fluopyram seed treatment alone.

In 2019, we conducted field experiments in Illinois, Indiana Iowa, Michigan, Wisconsin and Ontario, Canada to determine how fungicide and nematicide seed treatments, in-furrow and foliar applications will affect SDS and SCN. Three separate field experiments were established in each state in 2019 to i) test the efficacy of seed treatment fungicides for SDS management ii) evaluate the efficacy of nematicides seed treatments against SCN and SDS and iii) develop integrated management plan for SDS. We evaluated seed treatments including fungicides (ILeVo and Heads Up) and fungicides+nematicides (BioSt + ILeVO) applied on seed on SDS susceptible and resistant cultivars at each location for experiment 1. Nematicides BioSt, Aveo, Nemastrike, Clariva and ILeVO was included for experiment 2. A combination of seed treatment, cultivar, and seeding rate was tested for experiment 3.Data were collected at each location on plant population, root rot, root dry weight, foliar SDS incidence and severity, using standard protocols. We also collected soil samples for SCN counts and HG tying at planting at each location. SCN counting from those spring samples has almost finished and we are collecting fall samples. Soil samples from all locations have been sent to SCN diagnostics at University of Missouri, Columbia for HG typing. We are summarizing data from 2017 and 2018 field experiments. In brief, the preliminary data analysis showed that SCN seed treatments alone did not affect SDS foliar symptoms or root rot but when combined with ILeVO they provided the better disease and yield response than ILeVO alone.

We are working on determining relationship between SDS and soybean yield using meta-analysis approach. A total of 52 uniform field experiments conducted in Illinois, Indiana, Iowa, Michigan, Wisconsin, and Ontario Canada from 2013 to 2017 comparing crop protection products against SDS were analyzed using meta-analytic models to summarize the relationship. For each study, correlation and regression analyses were performed separately to determine correlation coefficients (r), intercept (ß0) and slope (ß1) and then summarized using meta-analysis. The overall mean correlation coefficient was -0.39 indicating yield was negatively correlated with FDX. That means yield will be decreased with increasing SDS foliar symptoms. The correlation was affected by disease level and cultivar with a greater magnitude in higher disease levels and with susceptible cultivars. The mean ¯ß1 was -21 kg/ha/%. In relative percent term, for every unit of FDX increase yield will be decreased by 0.5%. The result was presented in the annual American Phytopathological Society meeting held on August 3-7, 2019 in Cleveland, Ohio. A manuscript writing is in progress and will be submitted soon in Plant disease.

In 2018 and 2019, several hundred individual plants with different visual ratings of SDS from low to high were tagged in three farmer’s fields located in the Boone, Hamilton and Webster counties of the state of Iowa and the border rows of our 2018 microplot experiment at Iowa State University’s Hinds Research Farm in Story County. Disease was rated multiple times at weekly interval in those plants. Two hundred soybean plants with a range of SDS foliar symptoms were arbitrarily sampled (fifty plants from each farmer field and the border rows of the experimental plot at R6 growth stage for the Fv population density (in soybean root tissues and soil) study. We extracted DNA and ran qPCR, to quantify the pathogen in root tissue and determine the correlation with visual ratings. At the end of the season, the remaining labeled plants were harvested individually and yield component data including a total number of pods per plant, the total number of seeds per plant, total seed weight per plant and 100-seed weight per plant were collected from individual plants to correlate yield with the SDS severity. To determine the soil sampling protocol for determining SDS pathogen level in soil, we identified fields with low and high risk of SDS based on previous years SDS severity and collected samples in different time and from different soil zones in 2017. DNA extraction has been completed and DNA samples are being processed for qPCR in 2018. Muhammad Mohsin Raza, a PhD student shared with Dr. Leonor Leandro, is working on this project and summarizing data. He presented his result in NCERA and Southern Soybean Disease Workers meeting in Pensacola, FL in March 6-7, 2019.

We collected soil samples from ILeVO-treated and untreated plots from both resistant and susceptible cultivars at planting and after harvest to determine how ILeVO treatment affects F. virguliforme population and soil health in 2018 and and at planting in 2019. Midseason soil samples was also collected at V4. Samples were split in half and one half was used to quantify F. vilguliforme DNA concentration in soil using qPCR protocol identified in our previous study. The remaining samples were used to assess indicators of soil function and health, including soil physicochemical properties, enzyme activities, mycorrhizal colonization potential, and total nematode community assessment. Samples for soil health test are being processed in Dr. Nathan Kleczewski at University of Illinois and the other half to quantify F. vilguliforme DNA concentration in soil are being processed in Dr Martin Chilver’s lab at Michigan State University.

We completed field experiments in Iowa, Indiana, Michigan, Wisconsin and Ontario to investigate the effect of corn residue on SDS development. We compared two levels of residue removals and two tillage systems in corn and soybean rotation system. We recorded data on plant population, root rot, foliar SDS, and yield. We are collecting and analyzing data, and writing a manuscript. Two students (Grazieli Araldi Da Silva from Iowa State University and Amy Baetsen-Young from Michigan state university) are finalizing the manuscript and will be submitted soon for publication. Grazieli Araldi Da Silva working on this project for her PhD degree with Dr. Daren Mueller and Leonor Leandro at Iowa State University, recently graduated.

A manuscript entitled “Benefits and Profitability of Fluopyram-Amended Seed Treatments for Suppressing Sudden Death Syndrome and Protecting Soybean Yield: A Meta-Analysis” was been published in Plant disease (Plant Disease 102:1093-1100). In this manuscript, we complied from multiple locations evaluating ILeVO seed treatment for SDS management and yield response to the seed treatment using a meta-analysis approach. In summary, a 35% reduction in foliar disease and 4.4 bushels/acre (7.6%) increase in yield were estimated for fluopyram-amended seed treatment relative to commercial base seed treatments without ILeVO.

Fields with long-term fertility experiments established by Dr. Antonio Malarino, Professor Nutrient Management Research and Extension, ISU, in Northeast research farm, Nashua and Southeast research farm, Crawfordsville, Iowa, were selected to determine how soil potassium levels affect SDS in 2017. We collected SDS and yield data and analyzed in 2017. In 2017, plots with no potassium had less disease than the potassium applied plots. In 2018, the experiments were continued and we monitored those plots in Nashua for SDS at soybean GS R5.6 but no foliar symptoms were observed. We are gathering and analyzing data from 2017 and 2018.

We presented an update of SDS projects in NCERA meeting held in Pensacola, FL in March 5, 2019. We presented our research reports at annual APS meeting, winter meetings, ICM conferences, on Crop Protection Network, many state or province level talks, seminars, media interviews, talk in field days and conferences for farmers and also published in state newsletter articles, several media releases etc. Our information was also uploaded to SRII. The result from this study will have directly benefited soybean farmers in the North Central region and also establish foundation to address future research and management questions.

This project provides farmers with unbiased information on products that can be used as part of an IPM plan for SDS. As an example, some companies promote their products for SDS management (e.g., Mertect, HeadsUp, Fortix), but after careful evaluation, we are able to show farmers that these products actually are not effective at management of SDS. We will continue to evaluate products as they become commercially available.

The group is working towards identifying the risk of SDS in fields. We are still several steps away, but progress is being made in correlating inoculum and disease levels. We are also looking at other soil health metrics to fine tune this relationship.

We are evaluating other possible management strategies that could be incorporated into an IPM program. For example, there is some evidence that corn residue plays a role in SDS severity. We evaluated the effect of removing corn residue on SDS. We found that removing corn residue (leaves, stalks) did not affect SDS levels. We also evaluated SCN seed treatments since SCN can affect SDS severity. We found that SCN seed treatments do not affect SDS levels.

We are continuing to look at other possible management strategies (e.g., soil nutrient levels, improving soil health, cover crops) and how we can identify the risk of SDS in particular fields (this will help with seed selection and seed treatment choices before the season).

We take several different strategies for making sure the work being done on SDS is being communicated. We write journal articles to make sure the research community is aware of what we are doing, we write articles for the soybean checkoff community and Extension articles for ag business/extension agents through the Crop Protection Network. We also communicate about our research directly with farmers and ag business through extension events, social media, and media press releases.