Research Highlights

Early Planted Soybeans Can Recover From Herbicide Injury

Highlights:

• Early planted soybeans run the risk of injury from pre-emergence herbicide application.
• Illinois researchers have found most plants can recover from injury and stand loss with little to no yield penalty.
• Farmers may need to revise their herbicide management plan to keep weeds at bay through the season with early planted soybeans.

By Carol Brown

In many areas, farmers are planting soybeans earlier than their parents or grandparents ever did, and in some places, even before corn. Early planted soybeans have been known for higher yields, but when the seeds are in the ground longer, germination could be delayed due to cold, wet soils. This can increase the seeds’ duration of exposure to pre-emergence herbicides and reduce its ability to metabolize the herbicide, all of which can increase plant injury.

Illinois Extension weed specialist Aaron Hager and his team are increasing their understanding of best management practices when planting soybeans early, including weed control. His current research focuses on how much herbicide injury potential early planted soybeans can endure through a Soy Checkoff project funded through the Illinois Soybean Association.

The research project is in its third year with this cropping season. Behind the project is University of Illinois research specialist Logan Miller who studied this as part of his master’s thesis. 

“We planted soybeans in mid-April and mid-May with a pre-emergence herbicide application, with and without a cereal rye cover crop, which was new this year,” Miller explains. “The plots had different post-emergence applications: an early post-emergence, and a mid-post with and without a residual. We’re looking to see if there are any benefits to one application over another.”   

Trial sites are at the Crop Sciences Research and Education Center near Champaign. The team used 12 commercially available herbicide premixes with 10 active ingredients that encompass five site-of-action groups (Table 1). They applied each at their respective label rates immediately after soybean planting under no-till and with tillage. They included check plots with no treatments. By the end of the season the soybeans were able to recover from any early injury.

“One thing we’ve learned from this work is that it’s still advisable for farmers to use residual herbicides,” comments Hager. “These will always be important, especially when farmers are planting in late March to early April. There is a lot of growing season ahead. When that is coupled with weeds — such as waterhemp that can grow until the soybean canopy is fully formed — it highlights the need for the residual herbicides.”

Hager stressed that a key player in early season planting is environmental conditions, which will be different every year. A late frost can do more damage to a soybean stand than injury from a herbicide, he says.

“At the end of the growing season, there wasn’t much of a yield difference between the plants that saw early injury from the pre-emergence applications and the non-treated soybeans, nor was stand loss an issue,” Hager says. “Soybeans are an incredible plant. They can take a lot of stress and have the ability to recover.”

Early Soybean Planting Considerations

Advantages to planting soybeans early include increased yield and time savings, especially if farmers have a lot of acres to cover. They should check the weather forecast prior to applying a pre-emergence herbicide to early planted soybeans, as potential frost and timely rainfall events will be significant.

“During the research project, when we’ve planted early and applied a pre-emergence herbicide, we have had a rainfall event in a timely fashion,” Miller comments. “But planting in May hasn’t been the same. Some years we had no rain, which doesn’t do the pre-emergence herbicides any good.”

Other management factors to consider before deciding to plant early are maturity group, soybean variety, seeding rates as well as tillage and cover crop usage. Using treated soybeans is crucial with early planting as soybean seeds are in the ground longer before germination. The seed treatments ward off pathogens that lead to seedling diseases and insect damage.

Farmers also need to know the weed spectrum they see in their fields, which will dictate what types of herbicide to use. Hager says confirmation of glufosinate resistance in waterhemp was announced last winter in Illinois, which means they have documented resistance to every previously affected post-emergence corn and soybean herbicide. This is forcing farmers to rethink their herbicide plans. 

“Farmers may not have a viable post-emergence option,” remarks Hager. “If they need a PPO inhibitor to control their weeds, they will have to expect some soybean injury. But if they are averse to crop response and don’t need the PPO, there are alternatives to use in the early planting window.”

Hager says that farmers are facing multiple post applications of a residual herbicide, or a layered residual approach. After the pre-emergence application, they then apply the post-emergence residual herbicide at the appropriate time that will get them through to soybean canopy closure. About 10 days after that, they can apply the next residual treatment.

“Unfortunately, this is a practice that soybean farmers are going to have to consider,” he says. “We have also been looking at metribuzin, which can be a viable option, but the application rate has to be accurate.”

Before deciding to plant soybeans early, farmers should weigh the risks and benefits involved and their weed management system plays a strategic part. 

Additional Resources

Illinois Study Looks at Managing Weeds in Early-Planted Soybeans – SRIN article

Corn-Soybean Planting Order Could Impact Farm Revenue – SRIN article

Tackling Weed Control in Early Planted Soybeans – SRIN article

What to Plant First: Soybeans vs. Corn – SRIN article

Manage Weeds in Early Planted Soybeans in the Upper Midwest – GROW article

Herbicides and Resistance Management – GROW information page

Meet the Researcher: Aaron Hager University profile

The Soybean Research & Information Network (SRIN) is funded by the Soy Checkoff and the North Central Soybean Research Program. For more information about soybean research, visit the National Soybean Checkoff Research Database.

Published: Aug 3, 2026