The soybean cyst nematode (SCN) continues to be the most important soybean production constraint in South Dakota. SCN is difficult to manage because it inhabits the soil and can survive up to 10 years without a host, therefore it is not practically possible to eradicate SCN. However, SCN can be managed to keep the population density below damaging levels. Management of SCN requires a concerted effort that includes grower awareness, use of resistant/tolerant soybean cultivars, supplemented by nematicide seed treatments where SCN population density in the soil is high. We propose to continue to offer free SCN testing and educational material for South Dakota soybean producers with funding support for this project.

Objectives of the proposed project:
1. Support South Dakota soybean producers by providing a no-cost SCN analysis of soil samples from their farm(s).
2. Provide educational information on SCN management to producers.

• Growers test their soils for SCN and receive information on management strategies specific to their fields.
• Information on SCN management to be made readily accessible through various media models.

Updated October 28, 2022:
Objective one updates are as follows. The SDSU Plant Diagnostic Clinic has performed more than 140 SCN tests in the August to October time point. Roughly 25-30% of these samples have had egg counts equal to or greater than 10,000, qualifying them for HG testing. HG testing will be done on all samples that fall into the category over the next several months. We have one undergraduate student that is now trained in SCN extraction and testing.
Promotional work to fulfill objective two has been ongoing. In September, we participated in an extension webinar to educate producers about signs and symptoms of SCN. This was a joint webinar with Connie Strunk and Dr. Febina Mathew. Webinar title was Soybean Cyst Nematode; The Silent Yield Robber. Additionally, I co-authored an SDSU extension publication with Connie and Febina entitled "Know Soybean Cyst Nematode! Numbers Matter!" This publication was distributed on the SDSU Extension website.

Updated January 20, 2023:
Objective one updates are as follows. The SDSU Plant Diagnostic Clinic has performed 28 SCN tests in the November to January timespan. There are 6 HG type tests that we are currently preparing to perform. We have one undergraduate student that is now trained in SCN extraction and testing and will be learning the HG type testing protocol.
Promotional work to fulfill objective two has been ongoing. In November and December, we attended Local Foods Conference, AgHorizons, and AgOutlook. At each of these meetings, we promoted the importance of SCN testing and informed many producers about SCN for the first time. We are also promoting continued SCN testing at the Commerical Applicators Trainings occurring in January. Members of the Extension Plant Pathology group also attended the National Soybean Nematode meeting to learn new research and new approaches to SCN testing and management so that those can be utilized in South Dakota. Finally, SCN testing, and management was promoted to about 60,000 people through radio interviews with Pam Geppert at Dakota Farm Talk and Chuck Lagner at KWAT in November/December.

Updated April 26, 2023:
Objective one updates are as follows. The SDSU Plant Diagnostic Clinic has performed 40 SCN tests in the February to April timespan. HG type tests have begun. All 6 samples were increased beginning in March and finishing mid-April. Numbers are extremely high and two generation occurred in the 30-day increase period. Therefore, counting of cysts will not be complete until mid-May and then HG type results will be available to those growers. We have had one student performing SCN related samples throughout this academic year and will begin training a newly hired student in May.

Promotional work to fulfill objective two has been ongoing. SCN problems and testing was promoted to around 5,000 people in this quarter. Talks about SCN were given at 1 Commercial Applicators Training, 2 Private Applicators Trainings, 2 talks to CHS, Soybean Crop Hour through SDSU Extension, 1 talk to SD NRCS, 2 talks at Soy100, and 1 talk to Independent Applicators. The SDSU Diagnostic Clinic booth also attended the Watertown Farm Show, Soy100, and Independent Applicators Meeting to promote SCN awareness and testing. We were able to speak to several people about the importance of testing and to educate about SCN resistance and management at all of these events.

Updated July 30, 2023:
Objective 1: The SDSU PDC performed more then 50 SCN tests in the last quarter of this grant. We also performed 25 additional soybean disease tests. HG Type testing was completed with types 1.2.3.4.5.7 being found across South Dakota. Type 2, which is the PI88788 line, had nematode reproduction occurring in all HG Type tests. This year, we added a new SCN positive county for South Dakota, Aurora county.

Objective 2: SCN testing and the problems associated with resistance were promoted at both in-person talks (estimated reach of about 500) and on the Dakota Farm Talk radio channel (estimated reach is 55,500 people). Talks about SCN testing and how it is supported through this grant were given at several SDSU extension events this spring. The audiences included producers, Master Gardeners, other SDSU scientists, SDSU Extension personnel, and USDA researchers. Free testing and HG type testing were promoted on Dakota Farm Talk radio show in June as well.

Updated July 30, 2023:
More than 400 SCN tests were performed in the SDSU PDC for the 2022-2023 reporting period. Most tests were positive for SCN with the average egg count in the range of 2000-3000 eggs/100cc of soil. Overall, higher numbers of eggs were observed in this reporting period than the last. HG Type testing showed that about 20% of females in South Dakota are reproducing on PI88788 lines, the main resistance gene for SCN management.

Outreach and education about SCN and SCN testing was a main talking point for 2022-2023. We attended more than 15 events, reaching more than 10,000 people across South Dakota. Ten Extension talks were presented to a large range of audiences including producers, educators, crop consultants, and NRCS with an estimated reaching of 1000 attendees. A webinar, extension article, and three radio spots promoting free SCN testing were completed, reaching an estimated 125,000 people.

In total, 400 SCN and 7 HG Type tests were performed throughout the reporting period. The average egg count was 2000-3000 eggs per sample, which is higher than previous years. Samples were submitted from many counties in soybean growing areas of South Dakota, including a new SCN positive county, Aurora. Through HG Type testing, we found that about 20% of female nematodes were able to reproduce on the PI88788 lines, suggesting that South Dakota has less nematode resistance than other states where the average is 30-65%. However, this percentage could be flawed as many producers do not regularly re-test to monitor SCN numbers after receiving a positive SCN test.

The final results of the educational element of this project are that 130,000 people were educated about SCN, made aware of free egg counts and HG Type testing, and were educated about the dangers of SCN resistance to PI88788 and Peking lines through presentations, news articles, and radio spots. We attended and/or spoke at over 25 events throughout the reporting period throughout the state of South Dakota to raise awareness about SCN. We attended a diverse range of events to reach a larger number of producers. One webinar and one extension article were also completed to better educate about SCN.

Overall, SCN numbers are increasing in South Dakota as well as spreading to previously unreported counties. Due to drought years, numbers have increased and it is increasingly important to monitor SCN numbers and to submit samples for egg counts and HG Type tests so that researchers and extension can monitor the growing nematode resistance to PI88788 lines in South Dakota.

The current SCN management practices are not sufficient to effectively manage SCN. Use of resistant varieties is effective and affordable, but there are only two sources of SCN resistance genes that are currently available and > 95% of the SCN resistant cultivars have their resistance genes derived from one source, PI88788. This use of one source of SCN resistance has led to the rise of SCN populations that are now capable of reproducing on this type of resistance and are increasing (Tylka et al. 2016).
Soil testing for SCN is the first step in the management of SCN. A soil test informs the field manager the level of SCN in the field and the test comes with SCN management recommendations based on the level of SCN. Producers and crop consultants will continue to submit soil samples for SCN testing at no-cost. This incentive will encourage sample submission and each sample results will be communicated to the submitter with recommendations for management depending on the level of SCN found. For soil samples found with high SCN numbers (>10,000 eggs/100 cc of soil), additional Heterodera glycine (HG) type determination test will be done. High SCN population sometimes may indicate an HG type that is resistant to PI88788. A grower can then be advised to switch sources of resistance and use Peking and other sources of resistance as they become available.
We will continue to create SCN awareness, provide educational information and demonstrate effective SCN management practices through publications on the SDSU Extension website (https://extension.sdstate.edu), distribute pamphlets during field schools and similar agricultural events, radio advertisements, and interviews. We will continue to encourage producers and crop consultants to continue submitting SCN soil samples for SCN testing for testing at no-cost. This incentive will encourage sample submission, and each sample’s results will be communicated to the submitter with recommendations for management, depending on the level of SCN found.