Adapting for Successful Cover Crop Management

By Brogan Schanz, SWOF Field Program Representative: SE Iowa

For farming operations of any size, deciding to incorporate or continue using cover crops can have a lasting impact. Application methods, timing, and objectives all play a role in effective management—especially when it comes to termination. The ease and success of this step, along with its effect on the following cash crop, often determines whether farmers continue this practice. Unfortunately, there is no silver bullet for effective termination every time. Most years, we are at the mercy of Mother Nature. Because of this, most farmers quickly learn how crucial it is to evaluate the current conditions and adapt as needed. Even small adjustments can either make or break an application this time of year. This was particularly evident last spring when several producers discovered how even one change in their tank mix determined whether their pre-herbicide pass was effective. One case stood out more than others.

A clear difference in cover crop termination—one side of this SWOF-enrolled field shows full termination, while the other side displays only partial control.

In early summer, I noticed a distinct difference in a producer’s field—one side had a successfully terminated cover crop, while the other did not. Furthermore, the soybeans on the successful termination side were at least a whole trifoliate further along than those on the side of the apparent partially controlled application. After visiting with the farmer, I learned that the entire field had been treated the same way: rye was flown on at the same time in the fall, terminated with glyphosate (Roundup) on the same day the following spring, and soybeans were planted on the same day.  However, one small factor differed—just before spraying this specific field, the farmer ran out of methylated seed oil (MSO) crop oil and switched to a crop oil concentrate (COC) instead. That single change made all the difference. The acres treated with glyphosate, ammonium sulfate (AMS), and MSO displayed only partial control of the rye, while the acres treated with glyphosate, AMS, and COC achieved nearly 100% control.

Understanding the Impact of MSO and COC on Termination

Successful termination of a cereal rye cover crop in this SWOF-enrolled field after being treated with glyphosate, AMS, and COC.

Why did this happen? MSO-based crop oil products enhance herbicide effectiveness by breaking down and penetrating the plant’s waxy cuticle more quickly, allowing for faster herbicide uptake. This makes the tank mix "hotter" and typically ensures better control, which is why MSOs are a common choice for cover crop burndown applications. COCs, on the other hand, primarily help herbicides adhere to the leaf surface, giving them more time to penetrate rather than forcing rapid uptake (Peltier, Ikley, and Dahl, 2024).

Partial control of a cereal rye cover crop in this SWOF-enrolled field after being treated with glyphosate, ammonium sulfate (AMS), and MSO

At first glance, this information might suggest that MSO is always the best option for a cover crop burndown application. And in most cases, that assumption is correct. However, environmental conditions play a crucial role in determining which surfactant is more effective. According to Dr. Erin Hill and Dr. Christy Sprague from Michigan State University’s College of Agriculture & Natural Resources, cover crop burndown applications are most effective when air temperatures remain at or above 45 degrees Fahrenheit for several days (Hill & Sprague, 2024). Since most burndown applications occur in early spring when temperatures are cooler and cover crop plants are exhibiting less active growth, MSOs typically perform well, actively aiding the herbicide in entering through the plant cuticles.

However, in this specific case, the application was made later in the spring in warmer temperatures. When used in such conditions, MSOs can sometimes make tank mixes too "hot," causing the target plant to shut down before fully absorbing the herbicide. This reaction can temporarily stun the cereal rye, putting it into a dormant state as a stress response, leading to only partial control (Peltier, Ikley, and Dahl, 2024). This effect is similar to how MSOs can burn or injure non-target plants, such as cash crops, during in-season post-emergence applications.

Beyond this one example, we observed similar results with other producers, reinforcing the idea that in warmer conditions, switching from an MSO to a COC may improve termination success.

Key Takeaways for Cover Crop Termination

This does not mean that MSOs should not be used for cover crop burndown applications—far from it. Instead, it highlights the importance of adapting tank mixes based on environmental conditions. When conditions are cooler, MSOs generally provide the best control. But in warmer conditions, a COC may be a better choice to allow the herbicide to work effectively without triggering plant dormancy.

Following labeled rates and recommendations is always essential. Farmers should consult their trusted local agronomist for site-specific advice, as they can provide recommendations based on current conditions. The goal is not to reinvent the wheel but to learn from past experiences and enter the next season prepared to successfully adapt to whatever challenges arise.

Producers today must be more adaptable than ever before. While integrating cover crops adds another layer of complexity, those who successfully manage them often find their operations more resilient. Cover crops improve soil structure and reduce erosion, but no farmer will risk their cash crop’s success to achieve these benefits. And no one should be faulted for this mentality. For those using or considering cover crops, understanding how to manage them effectively is essential. Adaptation is a key part of every farming operation, and having the knowledge to recognize when and how to adjust will ensure long-term success.

Brogan Schanz
Field Program Rep.

As our field program representative for Southeast Iowa, Brogan Schanz works with farmers in eastern Iowa to implement practical conservation practices into their farming operations. He also provides support to referral partners. Brogan earned a Bachelor of Science degree in Forestry and Natural Resource Ecosystem Management from Iowa State University. He previously worked in retail agronomy assisting growers with input selection and ensuring their success in the field. Brogan grew up near Amana, Iowa. He and his family currently live in West Liberty, Iowa where he also helps on the operations side of the family farm.

Sources:
Peltier, A., Ikley, J., & Dahl, G. (2024, February 14). Strategic Farming: Let's talk crops session talks adjuvants for maximizing herbicide efficacy. University of Minnesota Extension. extension.umn.edu

Sprague, C., & Hill, E. (2024, April 22). Cover crop termination. Michigan State University Extension. canr.msu.edu