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Early Season Adjuvant Strategies – Cover Crop Termination

In the blog post “Early Season Adjuvant Strategies – Burndown”, details about what to consider for an effective burndown of weeds and the role of adjuvants was explained. As growers are becoming more aware of the importance of soil health, cover crops are increasing in popularity.

Cover crops provide a broad range of benefits to increase soil health and become increasingly common for commodity crops. Cover crops can prevent erosion, improve soil structure, activate soil microbes, supply nutrients to the following crops, suppress weeds, improve soil water availability, and break pest cycles. They can also be used for forage production. These benefits have made more growers consider the use of cover crops in the past few years.

Cover crops can be divided into winter-hardy cover crops like cereal rye, wheat, and clover, or cover crops that do not survive the winter like oats, brassica crops, ryegrass. The survival of a cover crop depends on many factors like the time of planting in the fall and the weather from seeding to spring. The winter-hardy cover crops need to be terminated before the cash crop is planted to ensure the yield is not impacted in the regular season.

Cover Crop Termination

Tillage is generally not the best option to terminate cover crops.  It destroys many of the natural benefits they provide. Herbicides are the most reliable and flexible option for cover crop termination, but they also have some risks. Cover crops often have a thick canopy; they are rapidly growing plants in the spring. That characteristic, combined with the typical lower temperatures at this time of year, leaves the door open for termination failure when herbicides are improperly applied.

Glyphosate is the most used herbicide for terminating cover crops. Other herbicides like 2,4- D, paraquat, dicamba, or blends thereof can also be applied. Glyphosate generally provides more consistent control in early spring under variable weather conditions than, for example, paraquat. It is recommended to add adjuvants listed on the herbicide label to the tank mix to improve overall efficacy.

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Cover crops provide a broad range of benefits to increase soil health and become increasingly common for commodity crops.

Cover crops provide a broad range of benefits to increase soil health and become increasingly common for commodity crops. 

Inclusion of 2,4-D or dicamba in cover crop termination programs is likely required to achieve sufficient control of legume-based cover crops. It can also broaden weed control during the growing season. Both of these herbicides are compatible tank-mix partners with glyphosate and can be used before corn or soybean planting. Applying 2,4-D or dicamba one to two weeks before planting corn and planting it deep enough, at least 1.5 inches, enhances crop safety. Be sure to read the herbicide label for pre-plant restrictions before soybean seeding for the various 2,4-D and dicamba products on the market. It is always recommended to read the label of the pesticide applied for rates and needed adjuvants.

Weather is an Essential Factor

Suboptimal weather conditions can reduce herbicide effectiveness. The following suggestions may help when planning the cover crop termination spray.

  1. Whenever possible, spray in the middle of the day in sunny conditions when daytime temperatures are above 55°F. Under these conditions, the cover crop is actively growing and will absorb the herbicide more effectively.
  2. Nighttime temperatures should stay above 40°F.
  3. To compensate for the lower temperatures, use the higher labeled rate range of herbicides and adjuvants.
  4. Check the spray carrier water quality to see if there is a need for a water conditioner to ensure herbicide effectiveness.
  5. Follow the herbicide label instructions for adding the appropriate adjuvants, the mixing order, and the application instructions, including spray volume, nozzle type, and environmental considerations. Increasing the spray volumes up to 15-20 GPA can help increase coverage in dense cover crops.
  6. The use of off-label adjuvants or the inclusion of additional herbicides may reduce spray efficacy. Use of non-recommended additives can cause antagonism reducing the effectiveness of the herbicides.
  7. Always check herbicide labels for planting restrictions for corn or soybeans following application to avoid injury to your cash crop.
  8. If excessive foaming is happening during mixing, adding an antifoam/defoamer will ensure proper application rates.
  9. After herbicide applications, use a tank cleaner so that no cross-contamination will happen during post-emergence applications.
Herbicides are helpful to terminate cover crops. Adding labeled adjuvants optimizes the herbicide effectiveness, ensuring the desired results.

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