Production Blog

On Cows and Cover Crops

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Don't discount the plant-back restrictions listed on the herbicides labels when planting cover crops for forage -- your livestock's health is at stake. (DTN/The Progressive Farmer photo by Barb Anderson)

ROCKVILLE, Md. (DTN) -- It may be tempting to ignore those pesky plant-back restrictions when you set out to plant some cover crops this fall for livestock forage.

Most farmers realize the EPA is unlikely to discover that the herbicide they used on their soybean crop wasn't legally labeled for the tillage radishes they planted three months later for fall grazing.

As long the radishes survive any lingering herbicide residues, there's no harm, no foul, right?

Not so fast, said Joe Sellers, beef specialist at Iowa State University Extension.

"I'm not sure we can continue to ignore the fact that there are restrictions to how we use some of these herbicides if we then follow up with an annual forage crop," he said in a webinar hosted February 9 by the Practical Farmers of Iowa.

At stake is the survival of your forage cover crop, but also the safety of your livestock, Sellers noted.

Growers who don't harvest or graze their cover crops can choose to ignore plant-back restrictions on the label -- all they risk is crop damage. But once that cover is used for forage, either by haying or grazing, things get more serious.

Plant-back restrictions on a herbicide label tell growers how long they must wait after herbicide application to legally plant the next crop in their rotation. The timelines are established by company tests examining the residue levels of the herbicide in various rotational crops.

These tests aren't pointless bureaucratic obstacles; they avert herbicide injury to the following crop, and they also protect the health of animals and humans who consume them.

Setting these residue levels for each crop is time-consuming and expensive for companies, which are unlikely to take on the enormously diverse world of cover crops available to farmers, Sellers pointed out. Most limit their studies to common rotational grain crops like corn, soybeans and wheat.

If the herbicide you used on your cash crop doesn't list a plant-back restriction period for the cover crop you selected, it falls under the "all other rotational crops" category on an herbicide label. This category usually defaults to a plant-back restriction of 18 months, Sellers said. Of course, that takes a fall planting and even a spring planting of your forage crop off the table.

Operating off-label means that the company assumes no responsibility for any herbicide damage to your forage crop. More importantly, if any residues are ever detected in your livestock or the people who eventually eat them -- or if either were to become sick -- you are legally responsible.

"It needs to be a concern that minute residues could show up in the meat if they start looking for them," warned central Iowa farmer Tim Palmer during the Practical Farmers of Iowa webinar. "All of this takes a tremendous amount of planning and foresight, basically planning at the beginning of the year what the end of the season is going to look like."

Extension and university scientists are trying to make this planning easier for you. Purdue University, the University of Wisconsin, North Dakota State University and Iowa State University have all put out charts and literature to help growers figure out which herbicides are safe to use ahead of which forage cover crops.

You can find them here:… (NDSU);… (ISU);… (Wisconsin), and… (Purdue).

You can also make your life a little easier by tweaking the kind of forage cover crops you choose, Sellers added.

Large mixes of cover crops can be tempting for growers. The variety of plant species can satisfy a number of soil and forage needs in one fell swoop, but these "cocktails" may complicate your farming, Sellers said.

"The more different combinations of species you put in there that are not on an herbicide label, the harder it will be to find an herbicide program to use on your [cash] crop," he said. "Many of the cocktail mix ingredients will fall under that 18-month plant-back restriction."

No need to let one herbicide's plant-back restrictions decide your entire forage and cover crop system, Sellers added. "Come up with a [grazing or haying] rotation where you can plant far enough out to get the herbicides you want and avoid weed problems, but still use your cover crops there," he advised.

For more information, see the Practical Farmers of Iowa webinar here:….

Emily Unglesbee can be reached at

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.



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Martin seeds
2/18/2016 | 9:12 AM CST
Good job here, Emily.