Cover Crop Termination Guidelines - Walnut & Indian Creek Watershed

By Dan Case, Watershed Coordinator



Dear Cover Crop Participant,


Thank you for participating in the Walnut and Indian Creek Watershed Project and the Iowa Nutrient Reduction strategy! We hope you are seeing the benefits from your cover crop planting, as most of the fields are looking GREAT! Your cover crop will protect your field from heavy spring rains which hit at a time when fields are most vulnerable to erosion! The root growth the cover crop provides not only holds the soil, but also allows water to infiltrate quicker into the soil profile, which reduces the amount of overland flow that leads to erosion. The same root mass also improves the health of your soil by feeding microorganisms which provide the glue to help build soil structure. Your soil will be stronger and healthier because of the cover crop, which could mean being able to plant when everyone else has to wait for their field to dry. Cover crops also tie up nitrogen and make it available to your future crop-the same nitrogen that could have leached away during those spring rains! This equates to money in your pocket and cleaner water in Walnut & Indian Creek!



Photo courtesy of Jason Johnson, Iowa NRCS

Cover crops do require management! We want you to have the best experience possible so PLEASE REVIEW THE FOLLOWING SUGGESTIONS!


1) Evaluate for winter kill –Cover crop species that may normally winter-kill can sometimes over winter in southern Iowa. It’s important to assess if a cover crop field has survived the winter to make informed management decisions. If the above ground cover crop is brown and near the soil surface and no green plant material is present then your cover crop winter-killed. Cover crops such as tillage radishes and oats typically winter kill and then no additional spring management is needed. Other cover crops, such as winter or cereal rye, winter wheat, triticale, and barley, consistently over-winter in Iowa.


2) Termination options – Herbicides, tillage or a combination of the two can be used to effectively manage cover crops in the spring. Keep in mind any tillage will reduce the effectiveness of the cover crop residue to protect against erosion and suppress weeds. Some additional considerations for both methods of termination follow:


Herbicide:

Stephen Eschenbach, UFC Agronomist and project partner, provides the following suggestions for successful termination with herbicide: For successful herbicide termination, make sure the plant has "greened-up", is actively growing, and has enough living surface area for the herbicide to work. Experienced farmers suggest spraying during the middle of the day and, if possible, spray when air temperature is at least 50F. Overnight lows of 50F or greater for 2 days prior to application and 2 days after application will help ensure speedy control. Unless you have experience, separate nitrogen application from a "burndown" herbicide application.


For best results, cover crops should be terminated 2 weeks before planting corn if at all possible, and to burndown rye grain, a 32-44 oz of Roundup PowerMax (or 50-64 oz of 4# active ingredient/gal equivalent glyphosate) would be recommended. Before planting corn, rye should not be allowed to exceed 6-8” in height to prevent excessive planting issues or nitrogen tie-up, which could lead to yield loss. Additionally, using corn seed treated with a good fungicide combination for Pythium seedling disease is also important. Seedling diseases can be worse on corn when planted into green rye. With an early spring warm-up, that might require an application in late March or early April. Allowing rye to get larger than this does potentially lead to greater risk of yield loss.


Before planting soybeans, rye termination timing is not as critical to prevent yield loss. Some growers even choose to plant their soybeans into standing rye and then spray after planting or after emergence to kill the rye. This can work well, and doesn’t seem to hurt soybean yields unless water is a significant limiting factor. Dry conditions may cause you to want to terminate rye earlier to preserve moisture for the soybean crop. Post emergence applications of Liberty, Enlist, or labeled dicamba products can be used to control broadleaf weeds in-season on treated soybeans in addition to using Roundup to control rye in soybeans that are Roundup tolerant. Some farmers may also elect to bale or chop the rye and plant soybeans or forage sorghums/sorghum sudangrass hybrids after removing the rye. This can also be effective and a profitable use of the cover crop.


Tillage:

Terminating cover crops with tillage can be somewhat effective, but may take more than one tillage pass. Wet periods can delay tillage to terminate cover crops and wet conditions following tillage can allow cover crop plants to survive tillage operations. Also, tilling a cover crop to terminate eliminates the erosion prevention benefit that the cover crop would usually provide in the early part of the growing season. Please check with the NRCS office before performing tillage to make sure you will be in compliance with HEL provisions!


3) Consider nitrogen needs – Cover crops effectively sequester nitrogen and as the plant residue breaks down


it will release its nutrients, making them available for the crop later in the season when it is most needed. However, there is the potential for lower available nitrogen early in the growing season, especially following an overwintering grass cover crop like cereal rye. To protect yield, farmers growing corn after a cereal rye cover crop may want to apply 40-60 lbs of nitrogen at or near corn planting, and this nitrogen is best utilized by the corn when applied near the row with the planter. This is not additional nitrogen, but within the farmer’s total fertilizer program.


4) Planting- Take some extra time to set up your planter. In general, planting into cover crops is a little different experience than what you might be used to. Extra attachments on no-till planters such as trash whips can tend to bind up in heavy residue. You may need to take off some attachments! Added strength from the increased soil structure may require you to adjust your down pressure and closing wheels. If you don’t have GPS on your tractor you may have a hard time telling where you have and have not planted, so be ready! If possible talk to another farmer who has experience planting into cover crops. If you’re prepared, planting into cover crops can be a beautiful thing!


5) Know crop insurance requirementsCrop insurance rules state that a cover crop in Zone 3 (western thir


d of Iowa) must be terminated by the day of cash crop planting. A cover crop in Zone 4 (eastern 2/3rds of Iowa) must be terminated within 5 days of cash crop planting. If using no-till, an additional 7 days is granted to either scenario. More information about insurance requirements can be found at www.rma.usda.gov/help/faq/covercrops2016.html.


6) Start planning now for cover crop needs this fall – Determine what cover crop(s) work with your current or planned crop protection program. Some residual herbicides have carryover restrictions for certain species of cover crops. Consult with your agronomist and/or cover crop seed representative to look at your specific management system with the integration of cover crops. Additional information can be found at www.weeds.iastate.edu/mgmt/2015/CCherbicides.pdf


Thank you for participating in the Walnut& Indian Creek Watershed Cover Crop Program! We hope you have a wonderful experience with your cover crops. If you have any questions please call the Soil and Water Conservation District or your local agronomist. Thank you and have a wonderful Spring!


Sincerely,


Daniel Case

Watershed Coordinator