The Effect of Wheat on Soybean Cyst Nematode Populations in Double-Cropping Soybean Production

CPN 5010. Published January 25, 2023. DOI: doi.org/10.31274/cpn-20230127-0

Leonardo F. Rocha, Southern Illinois University Carbondale; Mirian F. Pimentel, Southern Illinois University Carbondale; John Bailey, JCB Ag Research, Effingham, IL; Terry Wyciskalla, Wyciskalla Consulting, Nashville, IL; Dan Davidson, Davidson Consulting, Stanton, NE; Ahmad M. Fakhoury, Southern Illinois University Carbondale; and Jason P. Bond, Southern Illinois University Carbondale.

Summary

• Field trials were conducted from 2017 to 2018 to investigate the effect of wheat on soybean cyst nematode (SCN) populations in double-cropping soybean production.

• Trials were established in production fields located in South Central Illinois farms, closely simulating conditions experienced by local growers (Figure 1). From planting to harvest, most field operations were conducted by collaborating growers.

• Nine fields with three levels of initial SCN pressure (low, moderate, and high) were selected in South Central Illinois. Wheat was planted in strips alternated with strips that were maintained in fallow and free of weeds over winter and early spring (See Figure 2). Soybean was planted in all these strips after the wheat harvest in late Spring.

• SCN eggs were counted at four dates throughout the trials: at wheat planting, between wheat harvest and soybean planting, during soybean mid-season (R1 growth stage), and after soybean harvest.

• Soybean strips that were previously planted with winter wheat had SCN counts reduced by 31.8% in the mid-season sampling and by 32.7% after the soybean harvest.

• Double-cropping soybean with winter wheat can potentially suppress SCN field populations while providing additional farm income.

Introduction

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is widely distributed in all major soybean production areas of the United States (Tylka and Marett 2021), with the potential to cause 60% yield loss when susceptible soybean varieties are planted. SCN will often cause up to 30% yield loss without showing aboveground symptoms (plant yellowing, stunting, etc.), highlighting the importance of soil testing for SCN levels.

Double-cropped soybean is commonly planted in fields following winter wheat harvest in mid to late June. In Illinois, double-cropping has been more successful in the southern portion of the state, where favorable weather conditions allow earlier wheat harvest and soybean planting. Warmer weather in the fall season provides winter wheat an extended window for growth before exposure to freezing temperatures (Nafziger 2009). Predicted climate change and associated increasing temperatures may allow farmers to practice double-cropping in more northern areas where soybean is produced. Most acreage with the potential for wheat–soybean acreage is in Illinois, Indiana, and Eastern Ohio.

Research goals

• Evaluate the effect of wheat on SCN population densities in double-cropping soybean plots under field conditions in South Central Illinois.

• Identify what is causing SCN egg counts to be affected in double-cropping soybean fields.

The research

This study was conducted in production fields in South Central Illinois (Figure 1). These fields had various soil types and SCN pressure levels, allowing us to simulate conditions experienced by local soybean producers. Each field location covered 2.5 acres, with approximately twenty acres used for this research project. Each field location was divided into six strips: three were planted with winter wheat, while the remaining three were left fallow and weed-free over winter (Figure 2). After the wheat harvest in late spring, soybean was planted in all six strips.

SCN egg counts were assessed at four time points: at wheat planting, between wheat harvest and soybean planting, during soybean mid-season (R1 growth stage), and after soybean harvest. Data were subjected to statistical analyses to evaluate the effects of wheat on SCN egg counts.

Impact of wheat on SCN counts

In this study, SCN egg counts were similar in wheat strips compared with fallow strips at wheat harvest. SCN egg counts did not fluctuate significantly during the wheat growing season, probably because temperatures were mostly below what is required for SCN development and wheat is a non-host of SCN (Figure 3).

At the R1 growth stage of soybean (beginning of flowering), our data reflected a 31.8% reduction in SCN egg counts in wheat strips compared to fallow. Similar trends were observed at the soybean harvest sampling, where SCN egg counts were reduced by 32.7% in wheat strips compared to fallow strips (Figure 3).

How does wheat suppress SCN?

Soil samples with reduced SCN counts were used in a series of follow-up studies. Rather than being governed by a single mechanism, the suppression of SCN in soybean fields double-cropped with winter wheat is potentially linked to multiple factors. We analyzed the soil microbial community in those plots and identified improved soil microbial profiles in double-cropping soybean fields, with increased populations of beneficial organisms, some of which can parasitize SCN eggs and cysts. Finally, we observed higher concentrations of chemicals released by wheat roots and decomposing wheat stubble, which may also help to suppress SCN counts.

How can this research help you to manage SCN?

Double cropping soybean with wheat led to a reduction in SCN counts of over 30%, demonstrating a potential to suppress SCN field populations while providing additional farm income. Farmers growing full-season soybeans in South Central Illinois and other regions with similar growing conditions may benefit from introducing wheat as a winter crop to manage SCN. Incorporating wheat into double-cropping systems can help growers maintain SCN field populations under the damage threshold and reduce costs and losses caused by SCN, the primary yield-limiting disease in U.S. soybean production.

This research update is based on the work described in the following peer-reviewed research article

Rocha, L.F., Pimentel, M.F., Bailey, J., Wyciskalla, T., Davidson, D., Fakhoury, A.M., Bond, J.P. 2021. Impact of wheat on soybean cyst nematode population density in double-cropping soybean production. Frontiers in Plant Science 12: 640714. Article / Google Scholar

References

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Acknowledgements

Authors

Leonardo F. Rocha, Southern Illinois University Carbondale; Mirian F. Pimentel, Southern Illinois University Carbondale; John Bailey, JCB Ag Research, Effingham, IL; Terry Wyciskalla, Wyciskalla Consulting, Nashville, IL; Dan Davidson, Davidson Consulting, Stanton, NE; Ahmad M. Fakhoury, Southern Illinois University Carbondale; and Jason P. Bond, Southern Illinois University Carbondale.

Reviewers

Travis Faske, University of Arkansas; Alyssa Koehler, University of Delaware; and Daren Mueller, Iowa State University.

Photo credits

All photos were provided by and are the property of the authors, reviewers, and/or their respective institutions.

Sponsors

This project was funded by the Illinois Soybean Association Checkoff Program. This article is published by the Crop Protection Network with funding provided by U.S. soybean farmers through the United Soybean Board, the United States Department of Agriculture – National Institute of Food and Agriculture, and the Grain Farmers of Ontario through the Canadian Agricultural Partnership (CAP), a federal-provincial territorial initiative.

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