Timing Volunteer Corn Management in Soybeans

INSIGHTS

• Volunteer corn can reduce soybean yield if left untreated.
• Minimizing harvest loss and opportunities for germination can help reduce volunteer corn.
• Early control of volunteer corn in soybeans preserves maximum yield potential.

Introduction

Figure 1 Volunteer corn clump emerging in soybean field trial evaluating impact on yield, Slater, IA 2024.

Lodged corn can result in dropped ears and harvest loss. In addition to lost yield potential, ears or individual kernels emerging in the following year’s soybean crop can cause additional loss if not managed properly. Like other weeds, volunteer corn needs to be controlled quickly to prevent competition with soybeans for available resources. Volunteer corn can also attract egg laying insects that otherwise would not have been present, potentially elevating insect pressure in the next season. For example, corn rootworm beetles may be attracted to feed on pollen and silks of volunteer corn plants and then lay their eggs, potentially threatening the following year’s corn crop.

2024 Agronomy in Action Trial

A soybean trial was planted in 30-inch row spacings at Slater, IA to evaluate the impact of volunteer corn on soybean yield when present at specific densities and herbicide application timings. Corn ears were soaked in water to promote germination prior to being placed directly on top of soybean rows (Figure 1). Volunteer corn densities were established at a rate of 900, 1,800, and 2,600 ears per acre. In selected plots, the corn was sprayed at either 4- or 12-inch corn heights with Fusilade® DX herbicide at 8 oz/A and crop oil concentrate at 1% v/v. Soybean yield of each volunteer corn density and application timing was measured at harvest.

Results

Soybean yield was reduced by 4-15% if volunteer corn was left uncontrolled, and the higher volunteer corn ear densities had the most significant losses (Graph 1). Yield loss from volunteer corn was significantly reduced when the volunteer corn was controlled with herbicide application. Earlier application control of volunteer corn further reduced soybean yield loss from 4.3% to 2.3% with 12- and 4-inch applications respectively (Graph 2). Additionally, the 4-inch timing application resulted in a1.5 Bu/A increase in yield compared to the 12-inch timing.

Volunteer corn was established directly on the soybean row in this trial (Figure 2), creating a more severe level of yield reduction. If it had been placed between soybeans rows it might not have reduced yield as much, although volunteers would still compete with soybeans for resources and likely have a negative impact on yield.

Graph 1. The influence of volunteer corn density on soybean yield in the 2024 trial in Slater, IA.

Graph 2. The influence of volunteer corn control timings in soybeans averaged across volunteer corn densities in the 2024 trial.

Summary

Figure 2. High volunteer corn density at establishment (left) and at harvest (right) in the 2024 trial.

This trial affirms that early control of volunteer corn in soybeans provides the best chance of preserving soybean yield potential. Identifying corn fields with lodging or ear dropping can help prioritize soybean fields that may need timely volunteer corn herbicide applications the following year. It is important to understand the corn trait technology present in the prior grown corn hybrids to help determine if glyphosate or glufosinate may be effective for controlling emerging volunteer corn in that specific field. Fall and late spring tillage prior to planting in fields with large amounts of previous season corn harvest loss can help germinate and eliminate significant amounts of volunteer corn. No-till planting can sometimes minimize the amount of volunteer corn that germinates too. Volunteer corn should be monitored and managed to set the soybean crop up for the best yield potential.