Cover Crop Management

ROCKVILLE, Md. (DTN) -- A lot of novice cover croppers are heading into this spring, thanks to record prevented planting in 2019.

Some cover crops will winterkill, leaving only residue to manage in the spring. But for common overwintering covers like cereal rye, wheat or hairy vetch, a lot of work lies ahead before the spring crop can be planted.

With DTN meteorologists and others predicting a wet spring pattern for many parts of the country, terminating and managing cover crops should be on the top of farmers' to-do lists, scientists and veteran cover croppers told DTN.

Here are six tips for managing cover crops this spring.

1. TERMINATION TIMING IS KEY

There are a number of ways to terminate a cover crop: tillage, crimping, spraying the cover with herbicides before planting the spring crop, or planting the spring crop into a live, growing cover and spraying it shortly afterward, called "planting green," explained Sjoerd Duiker, a soil scientist from Penn State University.

For first-time cover croppers, and particularly those planting corn, terminating before planting is probably the safest bet, said Brian Corkill, who farms in northwest Illinois with his father and has been using cover crops for almost a decade.

If you choose this option, try to terminate the cover at least two weeks before planting to give it plenty of time to dry down before you run a planter through, Duiker said. He even recommends that farmers who plan on tilling the cover crop consider a herbicide pass first if the cover has grown very tall and thick before farmers can get into the field with tillage equipment.

Don't despair if wet or cold weather doesn't permit this timely termination, Corkill added. Planting into a living cover crop can actually help dry saturated soils, as the growing cover pulls moisture from the ground.

For this route, termination timing should range between the day of planting and no more than a day or two after, Duiker said. "You don't want that cover crop to continue growing after you planted, because then it is just a big weed competing with your main crop," he explained.

Corkill has found that soybeans in particular are very amenable to planting green.

"They're more flexible," he explained. "And in soybeans, a lot of biomass is better to suppress weeds -- a couple years ago, we didn't even have to do a later postemergence spray in soybeans because our rye cover crop was so good."

2. PICK THE RIGHT HERBICIDES

For grassy covers like cereal rye or barley, glyphosate should work just fine, Duiker said. Remember that glyphosate does its best work when temperatures are warm enough for plants to be actively growing, Corkill added.

In the early spring, when conditions can still be chilly, he aims to limit spraying to days when nighttime temperatures dip no lower than 40 degrees and the days climb up to near 60 degrees. "Then we would typically wait until midmorning and quit midafternoon, to pinpoint when the field is getting the most sunlight," he added.

When legumes and other types of cover crops are added into the mix, herbicide selection gets more complicated. Additional tank mix ingredients such as dicamba and 2,4-D may be necessary, Duiker said. Corkill usually treats his cover crop termination spray as a burndown, complete with added residual herbicides, he said.

See a Penn State University chart on herbicide options for terminating legumes here: https://extension.psu.edu/…

3. PROTECT THAT SEEDLING

One of the risks of a growing spring cover crop is that its residue or biomass could interfere with the critical period of germination for the spring crop.

For example, if growers plant too quickly after terminating a cover crop, especially a thick stand, the planter could have difficulty navigating through the stringy, tough residue. That's why experts recommend a two-week window, Duiker said.

"You can get 'hair-pinning' -- where the planter coulter or double disk openers can't cut through the cover crop residue," he explained. "So they push it into the seed slot, the seed is dropped on top, and as the cover starts to decompose, it releases acids and doesn't allow the seed to get good soil-to-seed contact and you get a poor stand."

Contact with decaying cereal rye residue can be especially detrimental to corn seedlings, thanks to a phenomenon called "allelopathy," where the decaying rye releases a chemical that inhibits the growth of the corn seedling.

This effect is not fully documented and is sometimes confused with another common concern with cover crops, that is, nitrogen tie-up from the decomposing grassy cover, Duiker and Corkill noted. But one thing remains certain: getting that seed furrow closed up and protected from the cover crop residue is key.

"Your planter needs to be in tip-top shape," Duiker said. Some growers use cover crop rollers or cultipackers used to smooth tilled soil, to crimp the cover ahead of the planter, he said. Corkill finds that his Precision Planting CleanSweep, which allows him to adjust the down pressure of the row cleaners, does a sufficient job of matting or tearing out covers to create a clean seed bed.

Soybean seedlings are especially good at coming up through heavy residue if they are seeded carefully, he added. "They might get a little leggy, but we've never had any issues with standability," he said.

4. WATCH NUTRIENT AVAILABILITY

Nutrient tie-up can be an issue with corn following a grassy cover crop like rye, both Duiker and Corkill warned. The effect is more problematic with a larger rye or wheat cover that has reached the boot stage before termination, Duiker noted.

As the cover is dying, microbial organisms will use nitrogen from the soil in the process of breaking down the cover crop, which can lead to nitrogen deficiency in a young corn plant.

Corkill and his father have switched to applying more of their nitrogen in cornfields in the spring before planting, in addition to a starter fertilizer at planting, to help combat this risk from their rye covers. Terminating the rye cover crop earlier, when it is under 6 inches tall, can also stave off this phenomenon, he said.

Legume cover crops, such as hairy vetch or clover, on the other hand, can be a nitrogen boon to a corn crop, Duiker said. "Those two types of covers should actually contribute nitrogen to the following crop as they decompose -- like a slow release," he said. A thick stand of hairy vetch can supply up to 100 pounds of nitrogen equivalent, and clover can supply up to 70 pounds, he said.

5. SCOUT FOR PESTS

Growers with cover crop stands should scout carefully for certain pests, particularly armyworms, cutworms and slugs, Duiker and Corkill said.

Armyworm and cutworm moths like to lay their eggs in grassy cover crop fields, which provide a good food supply for the emerging caterpillars. While they prefer the mature grasses, they will munch on emerging corn and soybeans as a last resort if everything else is dead, Corkill said.

He has found that planting green often works well for these insect threats. The slowly dying cover gives any slugs and caterpillars a feed option beyond the emerging corn or soybean seedling. Nonetheless, he has had armyworms soar past threshold levels in his emerging soybean crop before, which required insecticides.

Insecticide options for slugs are scarce, however. "But we find there are more natural enemies of slugs in a field if we do plant green, compared to terminating well before planting," Duiker said.

Corkill has also discovered that particularly lush stands of cereal rye can provide an alluring shelter and habitat for small mammals, such as voles, which can feed on corn or soybean seed, though he has never seen a yield loss from it.

6. DON'T GO IT ALONE

Managing cover crops, especially during a potentially wet, rushed spring, is not a one-person job, Corkill said.

He urged first-time cover croppers to reach out early to their farming network, such as retailers, agronomists or crop consultants, to create a plan and make sure everyone knows it.

"Definitely make sure you have conversations with retailers or whoever is doing your herbicide application," he said. "And if you're doing it alone, seek out information from consultants or agronomists, so you don't make a mistake and become discouraged from doing cover crops again."

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee

(PS/BAS/CZ)

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