This project addresses “soybean disease, nematode, insect pest and abiotic stress biology, management and yield loss mitigation,” a stated key area of research and outreach focus for ISA. A total of 36 to 45 different field experiments (four to five different studies in each of Iowa’s nine crop-reporting districts) will be conducted annually to determine the effectiveness SCN-resistant soybean varieties and nematode-protectant seed treatments. A comprehensive and multi-faceted communication effort will disseminate research results in print and electronic media and in interviews and presentations to Iowa soybean farmers.

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 three or four 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.

The soybean cyst nematode (SCN) is the most damaging pathogen of soybeans throughout Iowa, costing Iowa farmers tens to hundreds of millions of dollars in lost revenue each year through yield reductions. SCN was successfully managed into the decade of the 2000s by growing SCN-resistant soybean varieties in alternating years with corn, a nonhost crop. However, almost all (>95%) SCN-resistant soybean varieties available to Iowa soybean farmers were developed with a single breeding line named PI88788. SCN populations in fields throughout Iowa have developed high levels of reproduction on resistant soybean varieties due to exposure to resistance genes from PI88788 for two to three decades.

An additional challenge with SCN-resistant soybean varieties is that not all varieties provide the same level of SCN control, not even with SCN populations that are well controlled by the PI88788 SCN resistance. The genetic basis of SCN resistance is complex and still being elucidated by researchers. Some seed companies do not test the level of SCN control provided by their soybean varieties, and some obtain varieties from third-party genetics providers and do not do verify the SCN resistance of varieties they have licensed.

Greenhouse testing at ISU has shown that numerous varieties marketed as SCN-resistant allow moderate or higher levels of SCN reproduction and a few allow as much nematode reproduction as susceptible varieties. The situation exists because there is no legal definition or standard level of suppression of SCN reproduction required for a variety to be marketed as SCN-resistant, and no government testing program verifies the SCN resistance in soybean varieties sold to farmers.

New soybean varieties become available for Iowa farmers each year, and there is a recurring need to evaluate the SCN control provided by varieties that are marketed as resistant to SCN. These assessments are as important now as ever before because soybean varieties with new or improved herbicide resistance traits may have been rushed to market and may have diminished resistance to SCN. Also, there currently are a few new soybean varieties with SCN resistance from the non-PI88788 breeding lines Peking and PI89772, and it is likely (and hoped!) that more will become available each year. It is important to assess the SCN resistance and yield performance of these varieties with non-PI88788 resistance. Such results can confirm that the varieties are effective for use in managing SCN and are profitable to grow - information that will reassure farmers and encourage them to grow varieties with new sources of SCN resistance.

Beginning in the mid 2000s, nematode-protectant seed treatments became available that are marketed as providing protection against SCN. At least 10 such products currently are available on the market. Like SCN resistance claims made for soybean varieties, there is no standard of control and no official program or organization that verifies and evaluates the effects of nematode-protectant seed treatments on SCN.

Four to five different types of field experiments will be conducted in each of Iowa’s nine crop-reporting districts each year in the project described in this proposal. A resistant variety evaluation experiment will be conducted plus three or four experiments evaluating nematode-protectant seed treatments. The experiments will provide SCN control and yield data from hundreds of SCN-resistant soybean varieties and the most popular and newest nematode-protectant seed treatments. The results of the experiments will help Iowa farmers make the best SCN management decisions. Also, project personnel will create an annually updated extension publication listing the more than 800 SCN-resistant soybean varieties for use in Iowa, which will help farmers know what varieties are available for each growing season along with key agronomic characteristics of the varieties.

Update:
In the last six months (1 Oct. 2021 through 31 March 2022), we:
- compiled and prepared a publication titled “Soybean cyst nematode-resistant soybean varieties for Iowa,” posted it online in November 2021 - see https://store.extension.iastate.edu/Product/pm1649-pdf.
- harvested plots in all 9 SCN-resistant variety trial experiments and 27 seed treatment evaluation experiments to determine yields in October 2021.
- 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 2021.
- extracted SCN cysts, then eggs, from 3,240 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 2021 through January 2022.
- compiled and analyzed yield and SCN population density data from the SCN-resistant variety trial and seed treatment experiments in December 2021.
- 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 10, 2022 issue of the Iowa Farmer Today newspaper. The report also is available online - see https://store.extension.iastate.edu/Product/ipm52-pdf.
- published four articles in the ISU Integrated Crop Management Newsletter about the resistant variety list and the variety trial results:
1) “SCN-resistant Variety Trial Information Estimated to Have Provided Over $200 Million in Value to Farmers from 2011 to 2016” February 28, 2022, see https://crops.extension.iastate.edu/cropnews/2022/02/scn-resistant-variety-trial-information-estimated-have-provided-over-200-million
2) “Substantial Yield Suppression from SCN Seen in Soybean Varieties with Resistance from PI 88788 in 2021” November 11, 2021, see https://crops.extension.iastate.edu/cropnews/2021/11/substantial-yield-suppression-scn-seen-soybean-varieties-resistance-pi-88788-2021)
3) “Soybean Varieties for Iowa in 2022 with SCN Resistance Different from PI 88788” October 27, 2021, see https://crops.extension.iastate.edu/cropnews/2021/10/soybean-varieties-iowa-2022-scn-resistance-different-pi-88788
4) “SCN-resistant Soybean Varieties for Iowa in 2022” October 20, 2022, see https://crops.extension.iastate.edu/cropnews/2020/12/soybean-varieties-scn-resistance-other-pi-88788.
- began contacting seed companies to request seeds of SCN-resistant soybean varieties for 2022 field experiments in January-February 2022.
- contacted BASF, FMC, and Syngenta personnel for seeds treated with Ilevo, Zironar, and Saltro, respectively, for 2022 small-plot field experiments.
- began receiving seed from seed and seed-treatment companies for 2022 field experiments, and designed the 2022 field experiments and began packaging of seeds for the various experiments in March 2022.
- conducted final soil sampling of farmer fields throughout Iowa to allow for selection of the final 2022 experimental field locations in March 2022.

Update:
Project progress from 1 April 2022 through 30 September 2022 included:
- Received seed from seed and seed-treatment companies for field experiments in 2022, designed the 2022 field experiments, and packaged and organized the seeds for the various experiments.

- The company names and numbers of varieties (in parentheses) included in the 2022 SCN-resistant soybean variety trial experiments are as follows: Agrigold (12), Asgrow (13), Channel (8), Cornelius (3), Credenz (3), Dyna Gro (9), Federal Hybrids (3), Golden Harvest (8), Hoegemeyer (8), Jacobsen (4), Kruger (9), Latham (9), LG Seeds (15), Merschman (13), NK (18), Nutech (11), Pioneer (7), Stine (19), Xitavo (14), Don Mario (3), and Virtue (2). Most of the varieties tested in 2022 possessed SCN resistance from PI 88788 but the following companies had varieties with Peking SCN resistance (number of varieties in parentheses): Agrigold (1), Dyna Gro (1), Federal Hybrids (1), Hoegemeyer (6), Jacobsen (1), Merschman (1), NK (1), Nutech (5), Pioneer (2), Stine (7), Xitavo (1), and Don Mario (2).

- 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 191 different SCN-resistant soybean varieties in 2022.

- 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 Trunemco (from NuFarm).

- 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 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 began on October 5, 2022.

- In August 2022, we contacted 55 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 early November 2022.

Currently there are three options for managing SCN: 1) growing nonhost crops such as corn, 2) growing SCN-resistant soybean varieties, and 3) using nematode-protectant seed treatments on soybean seeds. The results of the experiments conducted in this project help Iowa soybean farmers decide which resistant varieties and seed treatments to purchase for use in fields infested with SCN. The results of the experiments conducted in 2022 are not yet available because not all of the end-of-season SCN soil samples have been processed and counted, but all work on the 2022 experiments will be completed by the end of calendar year 2022, after which planning for 2023 will commence. The report of 2021 variety trial experimental results and the 2021 list of SCN-resistant soybean varieties for Iowa are attached to this final report.

Economic Impact/Significance
• estimated profit to farmers from information produced in variety trial experiments from 2011-2016 = $66.0 million to $78.8 million (PDF file of report can be downloaded at www.card.iastate.edu/products/publications/pdf/20wp603.pdf). A similar level of farmer benefit would be provided 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 2011-2016 = 91:1 to 109:1