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Webinar outlines cover crop options on prevented planting acres

By Jean Caspers-Simmet

Date Modified: 07/08/2013 2:40 PM

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AMES, Iowa — Continued rains will likely to result in many prevented planting acres in Iowa and Minnesota with much of this ground planted to cover crops. A prevented planting and cover crop webinar on Friday answered questions about crop insurance, Conservation Compliance and agronomic concerns.
The webinar was sponsored by Practical Farmers of Iowa along with the Agribusiness Association of Iowa/Iowa Certified Crop Advisors, Natural Resources Conservation Service, Risk Management Agency and the Iowa Department of Agriculture and Land Stewardship.
Speakers urged farmers to keep in touch with crop insurance agents, the Farm Service Agency, the Natural Resources Conservation Service and input suppliers.
If farmers do use prevented planting, Jim Gillespie, IDALS Division of Soil Conservation, encouraged them to consider using a cover crop, building conservation practices or, better yet doing both, on their impacted land.
The final planting date for full crop insurance coverage in Iowa for corn was May 31 and for soybeans was June 15. After these dates farmers have several options, one being to leave the land idle. Planting a cover crop can help prevent erosion and tie up the nutrients in the soil, Gillespie said. Farmers may also want to consider building additional conservation practices on the impacted land, such as terraces, grass waterways and sediment control basins.
Bob Hartzler, Iowa State University Extension weed management specialist, said what herbicide has been applied could affect cover crops decisions.
“Products vary widely in the risk they pose to cover crops,” Hartzler said. “It's a complex issue, and there is not a lot of information to guide decisions. If you want to put cover crops on during prevented planting, a lot of these herbicides won't have had time to degrade.”
Hartzler cited a Penn State study which measured cover crop sensitivity to a range of atrazine rates. Sorghum-sudan grass was highly tolerant but cereal rye measured almost complete failure at a half rate of atrazine.
“It's unlikely anything other than sorghum-sudan grass would survive in fields that have a full rate of atrazine applied this spring,” Hartzler said.
Hairy vetch was the only broadleaf crop that didn't have a complete failure at a half rate of atrazine.
Herbicide label restrictions limit options for what can be planted.
“A herbicide label is a legal document,” Hartzler said. “What it specifies is what needs to be followed. Residues of herbicide could restrict establishment of cover crops, and you don't want to waste time and money trying to plant a cover corp and have it fail.”
Normally farmers don't plant cover crops this early, said Sarah Carlson of Practical Farmers of Iowa. This year, farmers are looking at two planting periods — immediate prevented planting after June 25 and fall time.
“We want to make sure that we plant the right cover crop, the correct way and at the right time,” Carlson said.
Farmers should check seed supplies now as some suppliers will quickly run out of some seed species. PFI has a cover crop business directory on its website at
“Successfully established cover crops will help to reduce weed pressure and also improve soil health,” Carlson said. “Since this is such a wide open opportunity to plant cover crops, we want to try mixes if they fit correctly.”
Timing is very important, Carlson said. Different species do well at different times. In late June to early July, warm season grasses and legumes like berseem clover or cow peas would work. Other legumes will work if planted later in July. Spring small grains such as oats, barley or rye will work. Winter versions of small grains must be planted in mid-August
A grain drill is the best way to plant a cover crop to make sure the depth is correct, Carlson said. For small seeded cover crops it works well to broadcast them on the soil surface and then harrow or cultipack.
“Good seed to soil contact is critical,” Carlson said. “Reduce soil disturbance as much as possible because July can be hot and short on moisture.”
Buckwheat, sorghum-sudan, millet, teff and sunflower like heat and will winterkill. Brassicas planted in July will bolt. A better option is to plant them after Aug. 1.
For farmers going to corn in 2014, rye and radish is a good option, Carlson said. Planted in August, radish in the row winterkills and the rye can be killed a few days before planting. For ground going to soybeans there are endless choices.