Planting Rate and Fungicide Application: Impact on Yield and Agronomic Response in Soybeans

TRIAL GOALS

Over the past decade, improvements in soybean genetics, planting technology and weed control systems have led to lower planting rate recommendations for soybean farmers.¹

While fungicide use in soybeans is steadily increasing,² some farmers wonder if fungicide is more beneficial in higher populations that have a higher potential for disease development or vice versa.³

The goal of this research was to determine how planting rate and fungicide application interact and affect yield and disease development in soybeans.

RESEARCH STUDY DETAILS

This research was conducted at the Crop Science division of Bayer FOCUS sites in Illinois counties Kendall, Woodford, McLean and Macon from 2019-2021.
32 soybean products from 2.2-3.9 maturity groups (MG) were planted, with different products used at different locations and in different years.
All seeds were treated with Acceleron® Seed Applied Solutions STANDARD and ILeVO® seed treatment.
Seeding rates ranged from 60,000 to 160,000 planted seeds per acre.
Four replications of this trial were planted at each location.
Fungicide application varied by location and trial year. All fungicides were applied at the R3 growth stage.
Standard fertility and weed management practices were followed.
The 2019 growing season was very cool and wet through early June, leading to delayed planting for many farmers. Hot and dry conditions were prevalent in July and August, and excessive rainfall returned in September and October.
In both 2020 and 2021, there was sufficient moisture in the early part of the growing season, but there were very dry conditions throughout August and into September.

BREAKING DOWN THE NUMBERS

On average, across populations in the three years in this research, fungicide application provided an average yield increase of over 5 bushels and delivered additional profit of $41.47 per acre (Figure 1).
The most profitable configuration was a planting rate of 120,000 seeds per acre combined with an R3 fungicide application (Figure 1).
Without a fungicide application, a seeding rate of 160,000 seeds per acre was required for maximum yield and profitability potential. This rate provided $42.60 less income per acre than the 120,000 seeds per acre rate with fungicide applied (Figure 1).
Disease pressure was also fairly low in this trial. Overall, fungicide application helped reduce disease development by around 20% based on general disease ratings (Figure 2). This rating incorporates both disease incidence and severity, with a rating of 1 indicating no disease incidence and low severity and 9 indicating the highest disease incidence and severity.

Figure 1. Average yield response of soybean to fungicide application and plant population (2019-2021).

Figure 2. Effect of fungicides on disease development in variable plant populations across three locations in 2021.

SUMMARY OF RESULTS

Here are some key takeaways from this study:

Higher populations can lead to increased yield potential but may also increase the risk of disease development.
The results of this study show that fungicide application at the R3 growth stage resulted in an increase in yield potential across planting populations, even when disease pressure was not high. Understanding how these benefits help contribute to return on investment is beneficial to help farmers get the most out of soybean products.
In this study, planting soybeans at populations of 120,000 to 160,000 seeds per acre combined with the use of a foliar fungicide at the R3 growth stage should be considered to help maximize both yield and profit potential.

Sources

¹ Pedersen, P. Optimum plant population in Iowa. Iowa State University. https://crops.extension.iastate.edu/files/article/OptimumPlantPop_000.pdf

² Geisler, L.J., and Miller, J.J. 2017. Managing foliar diseases in soybean. Nebraska Extension. https://extensionpublications.unl.edu/assets/html/g1862/build/g1862.htm

³ Porter, S. 2019. Five reasons to stop your higher soybean population. Illinois Soy Advisor. https://www.ilsoyadvisor.com/on-farm/ilsoyadvisor/5-reasons-stop-your-higher-soybean-population