The soybean cyst nematode (SCN) is Iowa’s most damaging soybean pathogen. Random survey results indicate that SCN is present in 75 to 80 percent of Iowa fields. Population densities (numbers) can increase 10- to 50-fold in a single growing season, and the nematode can survive dormant in the soil for a decade or more in the absence of soybeans. Yield loss due to SCN can costs Iowa farmers hundreds of millions of dollars in reduced soybean yields annually.
Currently there are three primary ways to manage SCN, by 1) growing nonhost crops such as corn, 2) growing SCN-resistant soybean varieties, and 3) using nematode-protectant seed treatments on soybean seeds.
This research project addresses ISA’s key area of research focus titled “Soybean disease, nematode, insect pest and abiotic stress biology, management and yield loss mitigation” as stated in the “Iowa Soybean Association (ISA) Request for Research Proposals from Iowa State University for 2020-2021 (FY21) Funding” communication distributed in March 2020. The results of the proposed research will help Iowa farmers choose SCN-resistant varieties and will illustrate the likely return on investment for using nematode-protectant seed treatments in SCN-infested fields in Iowa. This research continues to be necessary because new SCN-resistant soybean varieties and new nematode-protectant seed treatments are available to Iowa farmers every year.
SCN resistance involves more than one gene in the soybean plant, and the effectiveness of resistance in varieties developed from the common PI 88788 breeding line also is affected by the number of copies of a set of major genes. Consequently, not every SCN-resistant variety with PI 88788 resistance will have the same amount of resistance against SCN. Evaluating soybean varieties for SCN resistance can be accomplished in 30-day-long greenhouse experiments, but the SCN control results do not correlate well with results from the field. Also and most importantly, yield can only be assessed in field experiments.
In this project, SCN-resistant varieties will be evaluated for agronomic performance and nematode control in field experiments conducted throughout Iowa. The field experiments will produce information for Iowa soybean farmers to use to select resistant varieties that reduce or slow the buildup of SCN numbers and maintain or improve yields in SCN-infested fields.
Similarly, nematode-protectant seed treatments vary significantly in how well they suppress SCN reproduction and/or improve yields. These products cost farmers $15 or more per unit of seed. Experiments in this project will generate information for Iowa farmers on the effects of seed treatments on soybean yields and SCN numbers in fields throughout the state.
In summary, SCN-resistant soybean varieties vary significantly in effectiveness in suppressing SCN reproduction, and results of greenhouse experiments do not accurately predict nematode control in the field. This project will provide field data on yields and effects of SCN-resistant soybean varieties and nematode-protectant seed treatments in Iowa.

The overall goal of this project is to provide Iowa farmers with the best possible research-based information about resistant varieties and seed treatments for managing SCN. There are three objectives to achieve the goal stated above. The objectives are to study:
1) the agronomic performance and nematode control provided by SCN-resistant soybean varieties being 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

• list of SCN-resistant soybean varieties for Iowa farmers (ISU Extension publication PM-1649)
• report of results of resistant variety trial experiments (ISU Extension publication IPM-52) - printed and distributed as an insert in the Iowa Farmer Today magazine
• research articles published in scientific journals (ex. Plant Disease)

Updated April 1, 2021:
- Compiled and prepared a publication titled “Soybean cyst nematode-resistant soybean varieties for Iowa,” posted it online in November 2020 - see https://store.extension.iastate.edu/Product/pm1649-pdf.
- Harvested 3,240 plots in all 9 SCN-resistant variety trial experiments and 27 seed treatment evaluation experiments to determine yields in October 2020.
- Collected soil samples from every plot the variety trial and seed treatment experiments (3,240 samples total) to determine final SCN soil population densities in October 2020.
- Extracted SCN cysts, then eggs, from the 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 2020 through January 2021.
- Compiled and analyzed yield and SCN population density data from the SCN-resistant variety trial and seed treatment experiments in December 2020.
- 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 11, 2021 issue of the Iowa Farmer Today magazine. The report also is available online - see https://store.extension.iastate.edu/Product/ipm52-pdf.
- Published articles for the ISU Integrated Crop Management Newsletter about the “Soybean cyst nematode-resistant soybean varieties for Iowa” publication on November 23 (see https://crops.extension.iastate.edu/cropnews/2020/11/scn-resistant-soybean-varieties-iowa-numbers) and December 7, 2020 (see https://crops.extension.iastate.edu/cropnews/2020/12/soybean-varieties-scn-resistance-other-pi-88788).
- Published an article in the ISU Integrated Crop Management Newsletter about the results of the SCN-resistant soybean variety trial experiments on January 11, 2021 (see https://crops.extension.iastate.edu/cropnews/2021/01/isu-scn-resistant-soybean-variety-trial-program-results-2020).
- Began contacting seed companies to request seeds of SCN-resistant soybean varieties for 2021 field experiments in January-February 2021.
- Contacted BASF, Nufarm, and Syngenta personnel for seeds treated with Ilevo, Trunemco, and Saltro, respectively, for 2021 small-plot field experiments.
- Began receiving seed from seed and seed-treatment companies for 2021 field experiments, and designed the 2021 field experiments and began packaging of seeds for the various experiments in March 2021.
- Conducted final soil sampling of farmer fields throughout Iowa to allow for selection of the final 2021 experimental field locations in March 2021.

View uploaded report

View uploaded report 2

Updated October 15, 2021:
Project progress from 1 April 2021 through 30 September 2021 included:

- Received seed from seed and seed-treatment companies for 2021 field experiments, designed the 2021 field experiments, and packaged and organized the seeds for the various experiments. The variety names and numbers of varieties included in the 2021 SCN-resistant soybean variety trial experiments are from Agrigold (8), ASGROW (18), Beck’s (14), Channel (7), Cornelius Seed (8), Credenz (8), Corteva/Pioneer (9), Dyna-Gro (9), Federal Hybrids (8), Hoegemeyer (11), Innotech (5), Jacobsen (4), Kruger (7), Latham (12), LG Seeds (12), Merschman (12), NuTech (14), Stine (18), Syngenta/NK (14), and Xitavo (9).

- Set up, planted, soil sampled, and maintained nine field experiments located throughout Iowa to evaluate the yield enhancement and nematode control provided by 207 SCN-resistant soybean varieties in 2021 (same as in 2020 and 21 more than studied in 2019).

- Set up, planted, soil sampled, and maintained nine field experiments located throughout Iowa to evaluate the agronomic performance and nematode control provided by 3 different nematode-protectant seed treatments - namely Ilevo (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, began trimming the field research plots at the 36 total field experiments in preparation for harvesting.

- In late August, we contacted more than 50 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 2021.

Performance Metrics:
- number of different variety trial and seed treatment field experiments conducted in 2020 = 9 and 27, in 2021 = 9 and 27, respectively
- number of different soybean varieties evaluated in the variety trial experiments in 2020 = 207 in 2021 = 207
- number of different brands of seed evaluated in the variety trial experiments in 2019 = 19, in 2020 = 20
- number of plots planted, maintained, soil sampled, and harvested in 2020 = 3,024, in 2021 = 3,024
- number of SCN soil samples processed and counted in 2020 = 6,048, in 2021 = 3,024 as of October 14, with 3,024 more to be done after harvest is completed in October 2021
- number of Iowa farmers and agribusiness personnel who received a printed report of the variety trial experiment results in January 2020 and who will again in January 2021 = 46,000 each year

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 2021 are not yet available because not all of the experimental plots have been harvested by the date of this report and none of the end-of-season SCN soil samples have been processed and counted. The report of 2020 variety trial experimental results and the 2020 list of SCN-resistant soybean varieties for Iowa were uploaded to the database with the April 2021 report..

The research will benefit farmers by showing the best practices available for managing the soybean cyst nematode (SCN) in their fields.