Cover Crop Considerations

Take Precautions Against Seeding a Weed

Pam Smith , Crops Technology Editor
Clean seed is an important precaution while seeding cover crops, says Darrin Sass, Streator, Illinois. Here he custom seeds cereal rye into standing corn near Tuscola, Illinois. (DTN photo by Pamela Smith)

TUSCOLA, Ill. (DTN) -- Darrin Sass carefully lines the high-clearance Hagie into standing cornrows. The giant-bug-looking machine just barely pokes above tassels. Instead of spreading fertilizer or pesticides, the rig is outfitted with a Gandy box to hold cover crop seeds and drop tubes designed to spew them onto the ground below.

Sass, a custom applicator for S&S Farm Chemical, Inc., Streator, Illinois, is seeding cereal rye in some fields and a combination of oats and radish in others on this particular day. The whole idea is to give the cover crops a head start instead of waiting to direct seed following harvest.

Business, he said, has been a bit slower this season with the tightness of the farm economy. "Some farmers have come to the end of their EQUIP dollars for the practice," he noted. However, Sass has become a believer in the benefits of cover crops and plans to apply more of them to his own acres this year.

One thing he hopes doesn't slow down the practice is suspicion that cover crops might be contaminated with the aggressive weed species known as Palmer amaranth. In recent weeks, the discovery of Palmer amaranth seed contamination in native seed mixes in Iowa, Illinois and Ohio has led to questions about whether cover crop seed might also be a source of the weed. These outbreaks have been in conservation and pollinator plots, but have stimulated concerns about cover crops.

University of Iowa agronomists Bob Hartzler and Meaghan Anderson posted information about the situation this week. Read it here…

"We are not aware of any situations of cover crop seed used in Iowa being a source of Palmer amaranth, and have not heard of this situation in other Midwest states," the agronomists said. The risk, they said, is small in cover crops grown in Iowa because most cover crop species are winter annuals, such as cereal rye and oats. Palmer amaranth is a summer annual.

"Because of this difference in life cycle, cover crop species are harvested when there would be no mature Palmer amaranth present to directly contaminate the crop seed. The second reason is that most winter annual cover crop seed planted in Iowa is produced in Iowa, South Dakota and North Dakota. None of these states currently have widespread Palmer amaranth (not considering the introduction of Palmer amaranth in conservation plantings this season), therefore reducing the likelihood of contamination," they added.

Seed mixes are all the rage with some cover croppers these days. Hartzler told DTN that anytime more things go into a seed mix, you increase the likelihood of something you don't want being introduced.

"I would guess the risk of contaminated seed from other components would be similar to cereal rye if their production cycle was similar (planting and harvest dates) and production area," Hartzler said. "However, if some of the species were produced south of Iowa, I would be concerned."

Sass emphasized the importance of knowing the seed source, using certified seed and inspecting it before sowing. "Some of this farmer-raised stuff that's out there can contain things you might not want. Just don't do it," Sass said. "We are very particular about our seed sources."

Hartzler and Anderson point out that many times the weed seeds are winter annuals that can be easily managed with tillage and/or herbicides. However, they did note that the possibility of cover crop seed being contaminated with Palmer amaranth cannot be ruled out completely.

"If cover crop seed did contain this problematic weed, it would likely be due to seed being present in machinery used to harvest or clean seed, rather than plants growing in the cover crop seed field. In this situation, the number of weed seeds in the cover crop seed would be much lower than has been observed in conservation plantings across the state," they said in their release.

To learn more about managing Palmer amaranth in conservation plantings, go here:…

Pamela Smith can be reached at

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Pam Smith