Research Highlights

Research Highlights
The Effect of Wheat on SCN Populations in Double-Cropping Soybean Production

A double-cropping soybean field south of Carmi, White County, Illinois, in late July. Photo: Leo Rocha

From the Crop Protection Network

The soybean cyst nematode (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.

Figure 1. Field locations selected in Illinois to study the impact of wheat on soybean cyst nematode (SCN) in double-cropping soybean. SCN population densities were defined as high when more than 6,500 eggs per 100 cc of soil were present, moderate from 2,000 to 6,500 eggs per 100 cc, and low when less than 2,000 eggs per 100 cc.

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. 

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 researchers to simulate conditions experienced by local soybean producers. Each field location covered 2.5 acres, with approximately 20 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 the winters (Figure 2). After the wheat harvest in late spring, soybean was planted in all six strips.

Figure 2. (A) A picture showing strips separating treatments in the field trial. (B) Field trial setup used for each location, showing strips and subplots.

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), 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).

Figure 3. SCN egg counts (eggs per 100 cc of soil) over the four sampling periods. The lines are the average of wheat and fallow strips across all nine locations. The asterisk (*) indicates that the treatments had statistically significant differences in SCN counts at that sampling.

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. Researchers 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, they 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.

Other Resources

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. doi:

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. 

Published: Aug 7, 2023

The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.