Planting soybeans into field with cover crops

(Photo: Iowa Soybean Association / File Photo)

Mild winter could mean few delays for Iowa farmers

April 10, 2024 | Kriss Nelson

Iowa Soybean Association (ISA) farmer members are indicating that soybean and corn planting could begin as early as this week or next.

Paying close attention to planter set-up, planting conditions and seeding rates are just some of the planting tips to consider to achieve maximum yield. This includes the optimal soil temperature for planting at 50 degrees.

The latest Iowa Soil Temperatures map shows the majority of southern Iowa has hit the 50-degree mark with northern half trending warmer into the upper 40s.

On the state’s eastern side, Daron Oberbroeckling of Davenport is planning on starting his planting this weekend.

“As conditions allow, we will begin planting. We recently had between three and five inches of rain, so it is field by field for what is ready and what is not,” says Oberbroeckling. “We are planting green into our cover crops. The size of the cover crop doesn’t concern me. I have planted into planter-high rye before. We will plant, then terminate.”

Kevin McGrain, from Hornick on the western edge of the state, says he is still a week away from starting to plant.

“Our field conditions are very uneven,” he says. “Some are wet, some are dry and some are just right, so I am not getting too excited yet.”

Like other farmers in his area, McGrain has been busy getting equipment ready to go—specifically, his sprayer—so he can terminate his cereal rye.

“The rye is growing well, and that has me concerned,” says McGrain. I prefer to terminate my cover crops before I plant, but I'm not sure I will be able to do that this year. I have planted green before, but I prefer not to.”

Southeast Iowa farmer Mark McGrory, from Victor, took advantage of the warm-up last month to have his cover crops terminated.

McGrory was pleased with the growth of this cover crop despite dry conditions. His first cover crops were planted early last fall on 300 acres of corn, which was harvested in September and drilled directly behind the combine. He says those acres were his biggest cover crop.

“The rye did its job. We have the root mass and achieved what we wanted,” says McGrory.

As of Tuesday, the McGrorys were making their finishing touches on equipment preparations with both planters already loaded anticipating getting started this week.

Advice for managing cover crops this spring

Joe Wuebker, an ISA conservation agronomist for the west-central part of the state, recommends scouting fields now to get a firsthand look at what is happening.

“We should be scouting for a few reasons,” says Wuebker. “Timing and proper method of cover crop termination or for harvesting and grazing that cover crop. Realize your goals for your cover crops and have a good backup plan just in case.”

Wuebker added it is also a good time to scout for insect and disease pressures as we get into planting.

“With a mostly mild winter, there is a chance of some insect pressure, which should be monitored,” he says.

Ryan Johnson, ISA conservation agronomist and farmer in northwest Iowa, says the current stand of his cereal rye will not provide the biomass for weed control that he wants to achieve, making him apprehensive about terminating.

In addition to weed control, Johnson would like to have rye growing for any early spring rains.

“That living root would be able to uptake some moisture in the top inch that might help me get a better seed bed to plant into,” Johnson says.

There are also some concerns about the effect the matting of decaying cereal rye could have on emerging soybeans if there were a later spring frost.

“Two years ago, the dead rye mat acted like a blanket and made for the beans poking out above it to frost off more than compared to beans emerging in black dirt,” says Johnson. “For this reason, I am going forward with no-tilling soybeans into hopefully 12-inch cereal rye and terminating it the day after planting.”

If the forecast holds, he is planning on starting to plant corn this weekend but will be ready to plant soybeans when conditions in the field and cereal rye growth allow.

Evan Brehm, ISA conservation agronomist in eastern Iowa, says there have been issues with cover crops terminating – most likely due to applications done in less-than-ideal conditions.

“Cover crop fields have really taken off this late winter. With that comes excitement from seeing them grow,” says Brehm. “However, this also raises concerns with the cover crops getting too far ahead of us. With those concerns, I’ve seen several fields sprayed with herbicide to terminate the cover crops. As of early April, it’s hard to tell how effective this has been.”

Moisture is another consideration for the termination of cover crops for the 2024 growing season.

“This has me concerned a bit about termination timings,” says Brehm. I continue to promote planting soybeans green, but caution on planting corn green unless you are set up with a starter fertilizer. Termination sooner will allow moisture for the cash crop, but if terminated too early with cooler temperatures where it might not take effect, I would rather take my chances with a later application of herbicide and terminate after planting green.”

Tips for terminating cover crops

If you are still waiting to terminate cover crops here are some tips to follow:

Use glyphosate alone with a recommended rate of 28-42 ounces per acre, depending on the formulation

“Tank mixing other products can reduce the efficacy of glyphosate,” says Brehm. “Lower amounts with higher glyphosate formulations, higher amounts with lower glyphosate formulations.”

Be aware of temperature

Spray with sun and temperatures above 60 degrees with temperatures remaining above 40 degrees at nighttime.

Not only can cooler temperatures affect the efficacy of a burndown herbicide, such as glyphosate, but they can also hinder the herbicide's uptake in cover crops and weeds, so best common practices are important no matter the targeted plant to terminate.

If you must spray during cooler temperatures, Brehm advises that coverage is key, and this could require increasing the gallons of water per acre.


Although tillage is an option, and preferred by some first-time cover croppers, Brehm is advising against it.

“I’ve seen issues with burying the cover crop residue followed by an herbicide application. The problem here is that the cover crop is not fully terminated by the tillage, and the herbicide may not reach the cover crop because it will be under the soil,” says Brehm. “This could result in the cover crop emerging later. It could also cause weeds to be buried, making the herbicide less effective on them.”

If you have termination questions, reach out to an ISA conservation agronomist.