On Cows and Cover Crops

Herbicide Plant-Back Restrictions Matter

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

ROCKVILLE, Md. (DTN) -- Farmers can't afford to bypass those pesky plant-back restrictions when planting cover crops this fall for livestock forage.

"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," Iowa State University Extension beef specialist Joe Sellers told growers and livestock owners in a webinar hosted by the Practical Farmers of Iowa on February 9.

At stake is not only the survival of your forage cover crop, but also the safety of your livestock and meat consumers down the road, Sellers warned.


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 a cover crop is used for forage, either by haying or grazing, things get more serious, Sellers explained.

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; not only do they avert herbicide injury to the following crops, they also protect the health of the animals and humans who consume them, Sellers explained.

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, he said. Most limit their studies to common rotational grain crops like corn, soybeans, and wheat.

If a corn or soybean herbicide doesn't list a plant-back restriction period for the cover crop a grower has selected, that cover falls under the "all other rotational crops" category on the herbicide label. This category usually defaults to a plant-back restriction of 18 months, which of course takes a fall planting and even a spring planting of a forage cover crop off the table, Sellers said.


Operating off label means the company assumes no responsibility for any herbicide damage to the forage crop. More importantly, if any residues are ever detected in the grazing livestock or the people who eventually eat them -- or if either were to become sick -- the grower could be held 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 cover-crop growers. Purdue University, the University of Wisconsin, North Dakota State University, and Iowa State University have each 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: http://bit.ly/… (NDSU); http://bit.ly/… (Iowa State); http://bit.ly/… (Wisconsin), and http://bit.ly/… (Purdue).

Try to select forage cover crops with these restrictions in mind, Sellers suggested.

For example, growers often favor large mixes of cover crops, which can satisfy a number of soil and forage needs in one fell swoop. However, these "cocktails" can complicate legal forage options, 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 an entire forage and cover-crop system, either, 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: http://bit.ly/…

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

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.


Emily Unglesbee