Protecting Soybeans from Aphids, as Easy as (Rag) 1, 2, and 3

Final report for LNC15-370

Project Type: Research and Education
Funds awarded in 2015: $127,247.00
Projected End Date: 09/30/2019
Grant Recipient: Iowa State University
Region: North Central
State: Iowa
Project Coordinator:
Erin Hodgson
Iowa State University
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Project Information

Summary:

Advances in soybean breeding have produced varieties with single, double and triple gene combinations of soybean aphid host plant resistance. These naturally-occurring genes dramatically suppress aphid populations and will reduce the reliance of insecticides in soybean. Farmers using aphid-resistance genes will save on input costs and minimize negative effects to pollinators and beneficial insects associated with insecticides. 

To address both the short-term and long-term goals of soybean aphid management, our proposed project combines growth chambers, field cages and on-farm research in a collaboration that includes both soybean breeders, farmers, a non-profit organization and commodity organization. We propose a progressive and complementary process for screening new aphid-resistance genes against soybean aphid biotypes that have been discovered in the United States. 

Introduction:

Although soybean aphid can be patchy within fields and between growing seasons, it is considered the most economically important Iowa soybean insect pest since 2000. Soybean aphid can significantly reduce yield, and therefore regular scouting and timely foliar insecticides have been the primary way to protect yield. Advances in soybean breeding have produced varieties with single, double and triple gene combinations of host plant resistance for soybean aphid. These naturally-occurring genes dramatically suppress aphid populations and will reduce the reliance of insecticides in soybean. Farmers using aphid-resistance genes will save on input costs and minimize negative effects to pollinators and beneficial insects associated with insecticides. Documented pyrethroid resistance in some Midwestern states also stresses the importance of host plant resistance as a management tool.

Project Objectives:

1) We completed Objective 1 in 2016 (Year 1). Our results confirm that the Rag1+2+3 pyramid effectively manages all known soybean aphid biotypes. Our results indicate that Rag1+2+4 would be an effective management option for biotype-1, biotype-2, and biotype-3 soybean aphid, but had a negligible impact on biotype-4.

2) We complete our work on Objective 2 (Years 1-2). We have been using seed from increases developed by Brian Diers (University of Illinois), including access to several gene pyramids.

3) We completed Objective 3 (Years 1-3). Soybean aphid responded to resistant gene combinations in more realistic growing conditions similar to the laboratory testing. We worked with three commercial soybean farmers in northern Iowa and incorporated strip trials of host plant resistance each year. Aphid pressure was low, but overall, host plant resistance was an effective tool compared to susceptible soybean.

4) This project also had considerable extension efforts to communicate research findings to Iowa farmers. In 2018, we were a featured at a Practical Farmers of Iowa (PFI) field day in northern Iowa. We spoke about the use of host plant resistance to mitigate the impact of soybean aphid.

5) The funding to support this project helped train a graduate student, Erika Rodbell. On 23 April 2019, she defended her master’s thesis at Iowa State University and plans to continue work in sustainable agriculture.

Introduction:

 

Research

Hypothesis:

Advances in soybean breeding have produced varieties with single, double and triple gene combinations of soybean aphid host plant resistance. These naturally-occurring genes dramatically suppress aphid populations and will reduce the reliance of insecticides in soybean. Our hypothesis is fields with aphid-resistance genes will have fewer aphids than aphid-susceptible genes. Ultimately, farmers will save on input costs and minimize negative effects to pollinators and beneficial insects associated with insecticides.

Materials and methods:

Objective 1. Screen new aphid-resistant gene combinations. Biotype survival on new Rag gene combinations requires laboratory testing. We maintain four soybean aphid biotypes at Iowa State University and have sufficient growth chambers to test these biotypes on aphid-resistant varieties. Replicates of each variety will be artificially infested in the vegetative stage (V2-3) with 5 aphids and their population growth measured over 14 days. We predict that the Rag 1+2+3 will provide protection from all the currently identified biotypes.

Objective 2. Seed increase for the strongest aphid-resistant gene combinations. Field-scale evaluation outlined in Objective 3 will require a seed increase. In Years 1 and 2, soybean breeders Brian Diers (University of Illinois) and Asheesh Singh (Iowa State University) will generate seed increases of the best-performing Rag varieties. This could include double and triple pyramided gene combinations, within a non-GMO background. Varieties selected for the seed increase will depend on the results of Objective 1. Those varieties that performed as well as Rag1+2 will be included, along with Rag1+2. In this way, even if the new varieties do not perform as well, we will have sufficient supply of the Rag1+2 pyramid to include in our on-farm testing (Objective 3).

Objective 3. On-farm testing of aphid-resistant gene combinations. Working with both the Practical Farmers of Iowa (PFI) and the Iowa Soybean Association (ISA), we will identify six farmers to collaborate with us to test the varieties selected from our first two objectives. The goal of this objective is not only to measure the performance of aphid-resistant soybeans in an on-farm setting, but also to demonstrate this value to farmers and members of both organizations.

We will conduct listening sessions with our farmer collaborators leading up to 2017 and 2018 field seasons to gain a better understanding of their knowledge for soybean aphid management and learn more about their farming practices. During these meetings, we will review the objectives, describe the experimental design, and confirm everyone’s responsibilities. Our goal is to include three treatments with replications at each farm, including a 1) “best bet” Rag gene combination from Objective 1, 2) aphid-susceptible variety that is genetically similar to the best bet, and 3) the farmer’s standard variety.  

Objective 3a. Small cage studies. The performance of these new aphid-resistance varieties cannot be measured solely in a growth chamber. In Years 2 and 3, we plan to use caged plants to evaluate aphid performance (Figure 1f). Soybean aphid infestations can be highly variable in both time and place, and therefore, using caged plants will ensure that data can be collected every growing season. We have used this approach to demonstrate the value of the Rag1+2 over Rag1 or Rag2 varieties (Wiarda et al. 2012). This approach includes growing plants in small plots, caging ten plants with mesh around a PVC frame, and artificially infesting caged plants with field-collected aphids. By enclosing the plants, aphids cannot move away or become food for predatory insects; therefore, aphid populations increase quickly and treatment comparisons can be made more easily. At three locations, we will include four Rag gene combinations, or treatments, replicated four times (total of 16 cages at each location). The biotype(s) within Iowa likely vary by location, so will we attempt to spread out locations throughout the northern part of the state. At beginning bloom, each plant within the cages will be artificially infested. We will measure aphid abundance and yield.

Objective 3b. Strip trials. In Year 3, we will expand our on-farm testing for aphid-resistant genes and continue working with the farmers used for Objective 3a. Farmers will plant long strips (>300 feet) of the top two Rag gene combinations and a susceptible variety replicated four times (total of 12 strips at each location). We will measure aphid abundance over the entire growing season and possible interactions with other soybean pests, note natural enemy activity, and yield.

Objective 3c. Small plot efficacy evaluations. In Year 3, we will include the top two Rag gene combinations in the Soybean Aphid Efficacy Evaluation (http://www.ent.iastate.edu/soybeanresearch/content/extension) directed by Erin Hodgson. The performance of aphid-resistant genes will be compared to insecticidal seed treatments and foliar insecticides at two locations. We will measure aphid abundance over the entire growing season and possible interactions with other soybean pests, note natural enemy activity, and yield.

Research results and discussion:

Impacts

A journal manuscript summarizing Objective 1 was prepared and submitted to the Journal of Economic Entomology in March 2017. Erin Hodgson also was actively presenting and writing about host plant resistance for soybean aphid to farmers and people working in agriculture (2 Extension proceedings, 2 Extension newsletter articles, 15 Extension presentations, and 1 Extension Videos). Preliminary results from Objective 3a indicate aphid-resistant soybean suppressed the aphid population.

Accomplishments

We completed Objective 1 in 2016. Our results confirm that the Rag1+2+3 pyramid effectively manages all known soybean aphid biotypes. Our results indicate that Rag1+2+4 would be an effective management option for biotype-1, biotype-2, and biotype-3 soybean aphid, but had a negligible impact on biotype-4. We also completed the first year of work for Objective 3a in 2016. Soybean aphid responded to resistant gene combinations similar to the laboratory testing. A second summer of work in 2017 will confirm our findings.  

 

Research conclusions:

2019

Host plant resistance to soybean aphid can suppress outbreaks of this pest in North America and provide yield protection. Substantial effort has been made to support host plant resistance genes within the soybean germplasm. Aphid resistance (i.e., Rag genes) can provide season-long protection without impacting the agronomic performance of soybean. These genes are available through public and USDA soybean breeding programs, and are commercially available in limited quantities and maturity groups. Despite their efficacy, farmer adoption of soybean aphid-resistant varieties is low. The purpose of this study was to demonstrate how these varieties preform alongside soybean aphid susceptible varieties on commercial farms when exposed to naturally-occurring soybean aphid populations in realistic growing conditions. We recorded soybean aphid populations and yield for five different varieties of soybean from commercial and university sources. Varieties consisted of three soybean aphid-resistant varieties, conferred by Rag1+Rag2 genes, and two susceptible varieties. Despite low populations in 2017 and 2018, we observed soybean aphid-resistant varieties were effective at managing populations without consequence to yield. Indicating, the implementation of soybean aphid-resistant soybean in Iowa is not dictated by the performance of these varieties.

Participation Summary
3 Farmers participating in research

Educational & Outreach Activities

14 Consultations
4 Curricula, factsheets or educational tools
25 Webinars / talks / presentations
7 Workshop field days
2 Online-training videos

Participation Summary

1500 Farmers
300 Ag professionals participated
Education/outreach description:

During 2016 and 2017, I conducted a number of extension events with a focus on soybean aphid management. Some events were lecture style and some were field days, but most participants were farmers. I also wrote a few publications that talk about soybean aphid management. I am currently working on a regional field guide for soybean aphid management.

2018 Update

Research Publications

1) Varenhorst, A. J., S. R. Pritchard, M. E. O’Neal, E. W. Hodgson, and A. K. Singh. 2017. Determining the effectiveness of three-gene pyramids against Aphis glycines (Hemiptera: Aphididae) biotypes. Journal of Economic Entomology DOI: 10.1093/jee/tox230.

2) Rodbell, E. A., E. W. Hodgson, and M. E. O’Neal. Soybean cultivar containing a three-gene Rag pyramid efficacy trial. In preparation for the Journal of Economic Entomology.

3) Rodbell, E. A., E. W. Hodgson, and M. E. O’Neal. On-farm testing of aphid-resistant soybean in Iowa. In preparation for the Journal of Economic Entomology.

4) Koch, R. L., E. W. Hodgson, J. J. Knodel, A. J. Varenhorst, and B. D. Potter. 2018. Management of insecticide-resistant soybean aphids in the Upper-Midwest. Journal of Integrated Pest Management. DOI: 10.1093/jipm/pmy014.

Extension Publications

1) Hodgson, E. “2018 Insecticide evaluation for soybean aphid.” In ICM News. 28 January 2019.

2) Hodgson, E. W., and R. Koch. 2018. Soybean aphid management field guide for the north-central region, 62 pp. (2nd edition). North Central Soybean Research Program, Publication IPM 0060.

3) Koch, R., E. Hodgson, J. Knodel, and A. Varenhorst. 2018. Management of insecticide-resistant soybean aphids, 4. pp. North Dakota State University, Publication E1878.

4) Hodgson, E. W. Resistance management plan for soybean aphid, pp. 95-96. In Proceedings: 29th Annual Iowa State University Integrated Crop Management Conference, Ames, IA, 29-30 November 2017.

5) Hodgson, E. W. Resistance management for soybean aphid, p. 14. In Proceedings: Iowa State University Crop Advantage Series, Ames, IA, January 2017.

6) Hodgson, E. W. Resistance management for soybean aphid, pp. 97-99. In Proceedings: 28th Annual Iowa State University Integrated Crop Management Conference, Ames, IA, 30 November – 1 December 2016.

7) Hodgson, E. “Summary of soybean aphid efficacy evaluation for 2017.” In ICM News. 21 December 2017.

8) Hodgson, E. “Resistance management plan for soybean aphid.” In Integrated Crop Management News. 15 February 2017.

Extension Presentations for all three years: 2,188 contacts

1) Hodgson, E. W. #IPM: how do we build resilient, sustainable pest management crop systems? University of Minnesota Extension Crop Pest Management Short Course, Minneapolis, MN [325 people] 12 December 2018

2) Hodgson, E. W. Resistance management plan for soybean aphid. Iowa State University Field Agronomist Professional Development Workshop, Ames, IA. [22 people] 29 November 2016

3) Hodgson, E., and E. Rodbell. Host plant resistance for soybean aphid. Practical Farmers of Iowa Field Day, Marble Rock, IA. [22 people] 6 September 2018

4) Hodgson, E. W. Resistance management plans for soybean aphid. 2018 Iowa State University Extension and Outreach Crop Advantage Series Workshops.

  • Okoboji, IA. [45 people] 4 January 2018
  • Burlington, IA. [7 people] 5 January 2018
  • Storm Lake, IA. [18 people] 9 January 2018
  • Atlantic, IA. [32 people] 16 January 2018
  • Waterloo, IA. [2 sessions; 110 people] 18 January 2018
  • Iowa City, IA. [40 people] 24 January 2018
  • Davenport, IL. [2 sessions; 35 people] 26 January 2018

5) Hodgson, E. W. Soybean aphid bites back: update on pyrethroid resistance. Iowa State University Extension and Outreach Integrated Crop Management Annual Conference, Ames, IA. [2 sessions; 155 people] 29 November 2017

6) Hodgson, E. W. IPM and economic thresholds for insects. Iowa State University Extension and Outreach Ag Chem Dealer Update.

  • Iowa City, IA. [110 people] 21 November 2017
  • Ames, IA. [95 people] 13 December 2017

7) Hodgson, E. W. Resistance management for two key field crop pests. Iowa Soybean Association Research Conference, Des Moines, IA. [15 people] 8 February 2017

8) Hodgson, E. W. Resistance management plans for soybean aphid. 2017 Iowa State University Extension and Outreach Crop Advantage Series Workshops.

  • Sheldon, IA. [38 people] 4 January 2017
  • Okoboji, IA. [22 people] 5 January 2017
  • Storm Lake, IA. [6 people] 10 January 2017
  • Mason City, IA. [2 sessions; 75 people] 13 January 2017
  • Fort Dodge, IA. [2 sessions; 85 people] 18 January 2017
  • Le Mars, IA. [6 people] 24 January 2017
  • Denison, IA. [8 people] 26 January 2017

9) Hodgson, E. Soybean aphid management update. Northcentral Research Farm, Iowa State University, Kanawha, IA. [2 sessions; 40 people] 7 September 2017

10) Hodgson, E. Soybean aphid life cycle, biology and dynamics. SCN and Soybean aphid Workshop, Field Extension Education Laboratory, Iowa State University, Ames, IA. [20 people] 17 August 2017

11) Hodgson, E. Soybean aphid management update. Crop Management Clinic, Iowa State University Field Extension Education Laboratory, Ames, IA. [2 sessions; 22 people] 13 July 2017

12) Hodgson, E. Soybean aphid resistance management. Northwestern Research Farm, Iowa State University, Sutherland, IA. [3 sessions; 95 people] 12 July 2017

13) Hodgson, E. W. Resistance management for two key field crop pests. Iowa Soybean Association Research Conference, Des Moines, IA. [15 people] 8 February 2017

14) Hodgson, E., and M. O’Neal. Soybean aphid management update. Iowa Soybean Association Field Day, Iowa State University Field Extension Education Laboratory, Ames, IA. [35 people] 9 September 2016

15) Hodgson, E. W. Resistance management update for soybean aphid and corn rootworm. Iowa State University Extension and Outreach Crop Clinic.

  • Mason City, IA. [85 people] 9 December 2016
  • Northwood, IA. [115 people] 9 December 2016

16) Hodgson, E. W. Resistance management plan for soybean aphid. Iowa State University Extension and Outreach Integrated Crop Management Annual Conference, Ames, IA. [2 sessions; 150 people] 1 December 2016

17) Hodgson, E. W. Resistance management update for soybean aphid and corn rootworm. Iowa State University Extension and Outreach Ag Chem Dealer Update.

  • Iowa City, IA. [115 people] 22 November 2016
  • Ames, IA. [80 people] 7 December 2016

18) Hodgson, E. W. Management update for corn rootworm and soybean aphid. Titan Pro Kickoff Conference, Mason City, IA. [2 sessions; 75 people] 18 August 2016

19) Hodgson, E. Soybean aphid management update. BASF Field Day, Iowa State University Northeast Research Farm, Nashua, IA. [25 people] 17 August 2016

20) Hodgson, E. Soybean aphid management update. Crop Management Clinic, Iowa State University Field Extension Education Laboratory, Ames, IA. [2 sessions; 45 people] 14 July 2016

Learning Outcomes

Key areas taught:
  • field crop pest management

Project Outcomes

Key practices changed:
  • using host plant resistance

3 Grants applied for that built upon this project
2 Grants received that built upon this project
2 New working collaborations
Recommendations:

Soybean containing Rag1+Rag2 genes were effective at mitigating soybean aphid, confirming on a commercial scale. We found aphid abundance did not significantly vary by soybean variety or seed source. Meaning, across resistant soybean varieties and seed sources, soybean aphid resistant varieties are an effective source of protection from soybean aphid. Such consistent efficacy means that Iowa soybean producers can be confident in the protection their soybean aphid resistant soybean would provide. We observed no evidence of yield loss associated with pyramiding Rag1+Rag2, with soybean aphid susceptible and soybean aphid resistant varieties yielding similarly to each other. Further highlighting that commercially available resistant soybean varieties provide similar yield to soybean varieties already implemented by Iowa farmers.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.