By Dan Zinkand

Relentless rains this fall reinforced Dave Legvold’s commitment to seeding cover crops while sidedressing corn during V3 to V6 growth stages. “I’ve been measuring for the ark I’m going to need,” Legvold joked in disbelief as mid-September rains saturated the soil on his farm near Northfield, Minn.

Dave was one of 12 farmers and other ag professionals who shared their insight about interseeding cover crops into V3 to V6 corn, dealing with herbicide impacts on cover crops and using grassed waterways to control ephemeral gully erosion at meetings in July. The events were sponsored by the Iowa Corn Growers Association and the Oregon Ryegrass Commission, and were held at the farm of ICGA President Jim Greif and wife Sharon at Prairieburg, the Iowa Land Improvement Contractors Association demo farm at Mellbourne, and Dordt University’s Agricultural Stewardship Center near Sioux Center.

Dave and son Mark have been seeding cover crops for six years, and their success intrigues Ben Gleason, ICGA’s Sustainable Program manager. Gleason told the 85 people who attended the three events that he hears from Iowans who insist cover crops won’t work north of Highway 20 or north of Interstate 80. As the crow flies, the distance between Des Moines and Northfield, Minn., is 199 miles.

Seeding cover crops early in corn

Conventional wisdom also says a cover crop must be drilled for best stand establishment, which limits seeding until late September at the earliest, and that means cereal rye grain is the only default “choice.”

But wet falls like 2018 and 2009 can delay harvest and cover crop seeding, and reduce cover crop stands, says Dave, who grows corn and soybeans 30 miles south of Minneapolis. So in 2016, the Legvolds began seeding shade-tolerant, cool-season cover crops into V3 to V6 corn as they side-dressed nitrogen.

Mark bought two bulk spreaders designed for distributing salt on roads and driveways during Minnesota winters. He secured the bulk spreaders on the fertilizer toolbar with brackets, placing each spreader three rows in from the end.

Traveling at 7 mph sidedressing liquid 28% N, the Legvolds seed 15 pounds per acre of shade-tolerant, cool-season cover crops. The mix from Albert Lea Seed House contains around 8 pounds (59%) annual ryegrass, along with clover, radish and vetch. Throats on the bulk spreaders adjust to change the cover crop seeding rate.

Cost for the bulk spreaders was about $2,200, which pleases Mark, who jokes that he’s a tight Norwegian farmer. Dave says the Rice County (Minnesota) Soil & Water Conservation District spent about $16,000 for a single-purpose cover crop seeder for interseeding. On-farm research by students at St. Olaf College in Northfield, Minn., found the seeding coverage of the bulk spreaders was virtually the same as the $16,000 cover crop seeder.

Herbicide, cover crops and V3-V6 corn

Like many Iowa corn growers, Ohio farmer Matt Vantilburg battles waterhemp and marestail, weeds that residual herbicides can control. “Corn wants to be king,” says Vantilburg, agronomist for Vantilburg Farms at Celina. They use no-till and cover crops on all their 4,500 acres of corn and soybeans.

ADVANTAGES: Seeding cover crops into small corn could help overcome several major obstacles farmers cited during the Iowa Cover Crops Listening tour in summer. Jim and Sharon Greif use this Deere 1850 Air-Drill to seed cover crops.

With weed competition, corn can lose the battle for water, nutrients and sunlight, and become sick and scrawny, just like a “runt pig,” says Vantilburg, a certified crop adviser. Vantilburg Farms has used cover crops since 2006, sells cover crop seed, and custom-seeds about 20,000 acres of cover crops each year into standing corn and soybeans using customized, high-clearance sprayers.

Controlling tough weeds without killing cover crops seeded into V3 to V6 corn creates a challenge, Vantilburg says. Herbicide options for successfully interseeding cover crops into V3 to V6 corn include Liberty-resistant hybrids, which he says are a “very good option. Liberty will work, but it’s not a residual.”

Thus, later flushes of weeds can occur and will compete with corn. “If you are going to plant a cover crop, talk to your agronomist or someone who has planted cover crops successfully,” Vantilburg says.

Sioux County farmer Kirk Den Herder has been cover cropping since 2010 in northwest Iowa. “Weather permitting, I’ve been seeding every acre,” says Den Herder, who feeds cattle and grows corn and soybeans near Orange City. He attended the session at the Dordt University farm and says insight from the Legvolds and Vantilburg was helpful.

They recommend Verdict as a residual herbicide and using annual rye grass instead of cereal rye because cereal rye isn’t shade-tolerant. They advise interseeding covers earlier rather than later, so covers are established before the rows close.

They recommend working with an agronomist, scrutinizing herbicide labels and checking research from ag universities. Online resources that address V3 to V6 cover crop seeding and herbicides include spring 2019 research from Michigan State University and the 2019 Field Report by the University of Guelph and Ontario Ministry of Agriculture (see below.)

Other conservation practices help

As a relatively recent adopter of no-till corn and soybeans and seeding cover crops, northeast Iowa farmer Tim Recker recommends permanent conservation structures like grassed waterways for erosion control and soil health. His Recker Excavating does tiling and builds grassed waterways; he and brother Jim also grow seed corn.

The increasing frequency of intense rainstorms highlights the importance of permanent conservation practices like grassed waterways, terraces, riparian buffers and contour buffer strips, says Recker, a past president of Iowa Land Improvement Contractors Association. Once established and maintained, these permanent practices protect the land even when wet falls delay, reduce or prevent cover crop seeding.

Last spring, Iowa was one of six states included in a pilot program through the USDA Natural Resources Conservation Service’s Environmental Quality Incentives Program to help farmers and landowners manage ephemeral gully erosion by installing grassed waterways, terraces, water and sediment control basins and cover crops. In Iowa, farmer demand for the pilot was about $28 million, which was more than five times the $5 million in financial assistance Iowa NRCS received through the pilot, says Shawn Dettmann, NRCS assistant state conservationist for 28 northeast Iowa counties.

Iowa farmer Jim Greif doesn’t like taking land out of production for grassed waterways, but he places this choice into perspective. “If you’ve got anything more than flat ground, you need grassed waterways,” he says. “You’ve got to keep waterways so you can drive across the field.”

Recker agrees with that advice on waterway maintenance. “I mow it like a lawn so it looks like a lawn.” He seeds perennial ryegrass with a nurse crop of oats to establish grassed waterways.

Cover crop resources

Below is a selection of videos and publications to learn more about cover crop seeding:

Zinkand, a native of Sioux Center, Iowa, is a cover crop consultant who lives and writes from Salem, Ore.