SCN-resistant soybean varieties vary significantly in how well they suppress SCN.
There is no legal definition or industry standard level of suppression of SCN reproduction
required for a variety to be marketed as SCN-resistant. In addition to resistant varieties, there
are many nematode-protectant seed treatments for sale to Iowa farmers with no minimum
level of suppression of SCN reproduction required. The field experiments in this project will
provide data from throughout Iowa on the effects of SCN-resistant soybean varieties and
nematode-protectant seed treatments on SCN reproduction and yields.

The overall goal of this project is to provide Iowa soybean farmers with research-based
information about resistant varieties and seed treatments for managing SCN. There are three
objectives to achieve the overall project goal, namely to assess and study:
1) the agronomic performance and nematode control provided by SCN-resistant soybean
varieties marketed to Iowa soybean farmers
2) the effects of increasing SCN reproduction on yields of SCN-resistant soybean varieties
3) the effects of nematode-protectant seed treatments on agronomic performance and
reproduction of SCN on resistant soybean varieties

Project Activities / Experiments

#1. Compile a list of SCN-resistant soybean varieties for Iowa farmers
Each summer, more than 100 seed companies will be contacted and asked to provide basic
information (relative maturity, herbicide resistance, source of SCN resistance, iron deficiency
chlorosis or IDC rating) about the SCN-resistant soybean varieties they offer for sale to Iowa
farmers. The information will be compiled into a publication in October each year and made
available as a PDF file on www.soybeancyst.info and www.soybeanresearchinfo.com. The
information in the publication will be summarized and distributed in a press release, and an
article will be published online in the ISU Integrated Crop Management News newsletter
describing long-term trends in SCN resistance availability and diversity. Print and radio ag media
throughout Iowa will use the information in the press release and newsletter article to inform
readers/listeners. The SCN Coalition also will use the information in communications pieces.

#2. Evaluate SCN-resistant soybean varieties for yield and SCN control in field experiments
More than 200 SCN-resistant soybean varieties from dozens of brands will be evaluated in
experiments in three fields located across northern Iowa (varieties of relative maturity 1.0 -
2.5), three across central Iowa (relative maturity 2.0 - 3.5), and three across southern Iowa
(relative maturity 2.5 - 3.8). The experiments will be conducted in fields rented from private
farmers in the nine USDA crop-reporting districts in Iowa.
Yield and beginning- and end-of-season SCN data collected from the experiments will be
compiled, analyzed, and averaged for each location and summarized in a report published by
ISU Extension and posted online at www.isuscntrials.info, www.soybeancyst.info,
www.TheSCNCoalition.com, and www.soybeanresearchinfo.com.
The yield and SCN population density data for each variety in each experiment will be
presented in the report in bar graphs. The initial SCN egg population density and the HG type of
the SCN population at each experimental location also will be indicated at the bottom of each
table and graph of results. A printed version of the report will be direct mailed to 48,000 Iowans
as a special insert in the Iowa Farmer Today magazine each January.

#3. Evaluate nematode-protectant seed treatments for yield and SCN control
Field experiments will be conducted each year to assess the effects of two or three different
nematode-protectant seed treatments on SCN reproduction and soybean yields using the same
methods and in the same fields as the variety evaluation experiments described above. Each
nematode-protectant seed treatment will be compared to the base fungicide/insecticide seed
treatment with which it is sold. When possible, these experiments will be coordinated with and
complementary to on-farm strip trials with seed treatments conducted by agronomists in the
ISA Research Center for Farming Innovation.

Update:
In the last 6 months (1 October 2022 through 31 March 2023) we:
- compiled and prepared a publication titled “Soybean cyst nematode-resistant soybean varieties for Iowa,” posted it online in November 2022 - see https://store.extension.iastate.edu/Product/pm1649-pdf
- harvested plots in all 9 SCN-resistant variety trial experiments and 18 seed treatment evaluation experiments to determine yields in October 2022
- collected soil samples from every plot the variety trial and seed treatment experiments at the time of harvest to determine final SCN soil population densities in October 2022
- extracted SCN cysts, then eggs, from 3,024 soil samples collected from the SCN-resistant variety trial and seed treatment experiments at harvest, then counted the eggs to determine final SCN egg population densities from November 2022 through January 2023
- compiled and analyzed yield and SCN population density data from the SCN-resistant variety trial and seed treatment experiments in December 2022
- prepared a printed report of the SCN-resistant soybean variety evaluation experiment results, printed the report, and then had the report distributed to 48,000 Iowans as a special insert in the January 14, 2023 issue of the Iowa Farmer Today newspaper - the report also is available online - see https://store.extension.iastate.edu/Product/ipm52-pdf.
- published two articles in the ISU Integrated Crop Management Newsletter about the resistant variety list and the variety trial results:
• Tylka, G. 2022. High reproduction of SCN populations on PI 88788 resistance is frightening. Iowa State University Integrated Crop Management News (28 October 2022). https://crops.extension.iastate.edu/cropnews/2022/10/high-reproduction-scn-populations-pi-88788-resistance-frightening
• Tylka, G. 2022. More soybean varieties with Peking SCN resistance for 2023, but more needed. Iowa State University Integrated Crop Management News (22 November 2022). https://crops.extension.iastate.edu/cropnews/2022/11/more-soybean-varieties-peking-scn-resistance-2023-more-needed
- began contacting seed companies to request seeds of SCN-resistant soybean varieties for 2023 field experiments in January-February 2023
- contacted BASF, FMC, and Syngenta personnel for seeds treated with Ilevo, Avodigen, and Saltro, respectively, for 2023 small-plot field experiments
- began receiving seed from seed and seed-treatment companies for 2023 field experiments, and designed the 2023 field experiments and began packaging of seeds for the various experiments in March 2023
- received 53 Peking varieties to include in variety evaluation experiments in 2023, which is up from 27 in 2022
- conducted final soil sampling of farmer fields throughout Iowa to allow for selection of the final 2023 experimental field locations in March 2023

Update:
Project progress from 1 April 2023 through 30 September 2023 was as follows:

- Received seed from seed and seed-treatment companies for field experiments in 2023, designed the 2023 field experiments, and packaged and organized the seeds for the various experiments. The 33 companies with varieties included in the 2023 SCN-resistant soybean variety trial experiments are as follows: AgriGold, Asgrow, Beck, Brevant, Channel, Champion, Connect, Cornelius, Credenz, Dyna Gro, Four Star Seed Co., FS HISOY, Golden Harvest, Hoegemeyer, Impact, Innotech, Jacobsen, Kruger, Latham, Legacy Seeds, Legend, LG Seeds, Loyal Brandm, Merschman, Mustang, NK, Nutech, P3 Genetics, Pioneer, Rob-See-Co, Stine, Sunrise, and Xitavo.

- Most of the varieties tested in the 2023 variety trial experiments possessed SCN resistance from PI 88788, but the following 23 companies had varieties with Peking SCN resistance in the experiments: Agrigold, Asgrow, Beck, Brevant, Champion Seed, Connect, Dyna Gro, FS HISOY, Golden Harvest, Hoegemeyer, Impact, Innotech, Jacobsen, Latham, Legacy, Legend, LG Seeds, Loyal Brand, NK, Nutech, Pioneer, Stine, and Xitavo.

- Set up, planted, soil sampled, maintained, and prepared to harvest nine field experiments located throughout Iowa to evaluate the yield enhancement and nematode control provided by 196 different SCN-resistant soybean varieties in 2023.

- Set up, planted, soil sampled, maintained, and prepared to harvest nine field experiments located throughout Iowa to evaluate the agronomic performance and nematode control provided by three different nematode-protectant seed treatments, namely Ilevo (from BASF), Saltro (from Syngenta), and Avodigen (from FMC).

- Extracted SCN cysts (egg-filled, dead SCN females), then eggs, from soil samples collected at planting from all 9 resistant variety evaluation experiments and the 27 seed treatment experiments and counted the eggs to determine initial SCN egg population densities.

- In early September, the field research plots at the 36 total field experiments were end-trimmed in preparation for harvesting, which was completed in October 2023.

- In August 2023, we contacted 60 seed companies and gathered information about SCN-resistant soybean varieties to use to update the ISU Extension publication titled “Soybean Cyst Nematode-Resistant Soybean Varieties for Iowa”. This publication will be compiled and released in PDF format by the end of October 2023.

The research conducted in this project is farmer-focused applied research that is unique in Iowa in that SCN-resistant soybean varieties and nematode-protectant seed treatments are intensively evaluated under real Iowa field conditions and nematode data are collected from each individual 4-row research plot at the time of planting and again at the time of harvesting. The intensive-scale information emanating from these experiments is not available anywhere else in the U.S. The research results give Iowa soybean farmers first-hand information generated in their state about the performance that can be expected when these SCN-resistant soybean varieties and the nematode-protectant seed treatments are used.

Project deliverables include ISU extension publications, scientific research papers,
online newsletter articles, and online and in-person presentations. The printed variety trial
report will reach 48,000 Iowa farmers and agribusiness personnel annually.
The increased income of Iowa farmers resulting from use of information from SCN-resistant
variety evaluation experiments in 2011 to 2016 was estimated by ISU ag economists to be $86
million to $205 million, which represents a 119:1 to 283:1 return on investment on the checkoff
funds that were provided to support the research during those years. A similar level of farmer
benefit would be provided in each year of this proposed project.

Economic Impact/Significance
• estimated economic value to farmers of information from variety trial experiments from
2011 to 2016 = $86 to $205 million (published report can be downloaded here). Farmer
benefit would be similar or greater in each year of this proposed project.
• return on investment on $725,000 of Iowa soybean checkoff funds provided to support the
variety trial experiments from 2011 to 2016 = 119:1 to 283:1