• The right cover crop choice depends on desired goals, seasonality of species and herbicide rotational restrictions.
• The Midwest Cover Crops Council has a decision tool that helps select cover crop species based on location, goals, and planting date.
• When choosing cover crop species, consider any residual herbicide applications done this spring and their potential injury to the species selected.
• Some cover crop species will winter kill while others will require tillage or an herbicide application to terminate them.

Choosing the right cover crop species for prevented-plant acres depends on the desired goal, seasonality of species to be planted (cool season or warm season crop) and whether herbicide rotational restrictions exist.The Midwest Cover Crops Council has designed a tool that makes the choice somewhat effortless while prioritizing up to three goals you wish to accomplish by planting a cover crop (Image 1).

 Image 1 below: Midwest Cover Crops Council Row Crop Decision Tool criteria selection.

Once the state, planting date, harvest date, drainage information, flooding potential, and 3 goals are selected, the tool generates and ranks the possibilities.The choice essentially comes down a compromise of the desired goals.Do you want the cover crop to add nitrogen to the soil, do you already have nitrogen applied and want to trap this nutrient for the next crop, or is weed control most important to the field in question? These are just a few of the possible goal choices the tool provides.

As an example on how to use this tool, let’s assume that the farm is in Stephenson County Illinois and it can be planted by June 15^th. The field is moderately well drained, has a 2/3 nitrogen rate already applied and has no herbicide restrictions that apply.The outcome would look like the image below (Image 2). Note the rankings from 1-poor to 4-excellent for each of the chosen goals.

Image 2 below: Midwest Cover Crop Council Cover Crop Choices for Stephenson County Illinois with a planting date of June 15^th.

When considering the first of the three chosen goals which is to trap the applied nitrogen for use by next year’s crop, species that have fibrous or taproot root systems that penetrate the top 12” of soil make the best choice.  Grass crops such as Japanese Millet, Pearl Millet, Sorghum-Sudangrass, Sudangrass, Winter Triticale would be the best choices for deep fibrous roots.  Choosing the best mix, if you desire multiple species, would result in a 60:40 mix of ryegrass and oilseed Radish.  One thing to keep in mind is cover crop termination.  Some cover crop species will winter kill (fall frost) while others will require tillage or an herbicide application to terminate them and prep the field for next years planting.  Consider that crops such as oilseed radish that have large taproots and can effectively fracture shallow to deep compaction and trap nitrogen may require significant tillage to uproot and prep the field for next year.

What if I already sprayed a residual herbicide on these acres?  

To further complicate matters, many of the potential prevented-plant acres have received a residual herbicide application this spring.  To date, most of the potential prevented-plant acres were intended to be planted to corn.  Many of the most common herbicide mixes contain a group 15 (acetamide) herbicide in addition to atrazine (group 5).  The rotational restrictions to many grass species following a group 15 herbicide is 4.5 months while atrazine rotational restrictions can vary based on species.

Many who choose a cover crop will not want to wait until the rotation interval is complete to plant the cover crop, especially when capturing nitrogen or providing erosion management is a primary reason for planting.  A common-sense approach to planting may be to choose an economical species from the Midwest Cover Crop Council decision tool that will fit the need of the farm.  Delay planting at least 4 weeks from the herbicide application would be necessary to reduce the amount of residual herbicide remaining in the soil.  Then plant a small portion of the cover crop and wait 10 days after emergence and evaluate injury.  If no injury, plant remaining cover crop acres.  If the cover crop emerges injured or stand is reduced, wait two additional weeks and try again.

Lastly, the use of these cover crops as a forage or hay is prohibited.  The appropriate herbicide rotational interval to ensure herbicide residues are below thresholds may not have been met to safely feed to animals.  Additionally, this use may void the previous decision to take prevented-plant as this may be considered a true crop. For more information on cover crop selection or herbicide plant-back restrictions contact your local FS crop specialist.