Go Kill It: Tips for Terminating Cover Crops with Limited Glyphosate

Whether it’s to increase soil organic matter, reduce erosion, or get a secondary source of nitrogen, more farmers are turning to cover crops to reap the benefits they bring. Between 2012 and 2017, cover crop acreage increased 50%, according to the USDA Census of Agriculture. SARE survey data from 2019-2022 echoed the same trend, showing a 38% increase in cover crops over four years. 

As cover crop acreage expands across farms and geographies, more farmers are looking for expert management advice – particularly when it comes to termination. Whether you’re an experienced cover cropper or new to the practice, planting green or tilling your covers, the termination process is the single most important driver of cover crop success. 

But what happens when glyphosate prices skyrocket and supply chain issues limit access? You need to prioritize your herbicide use. For tips to make every drop count, we turned to the agronomist experts in our recent roundtable Terminate with Confidence

1 Consider How Much Growth You Have

“Your cover crops have been working hard all winter, fixing nitrogen and holding soil in place,” explains agronomist Sarah Carlson, Strategic Initiatives Director, Practical Farmers of Iowa. “As you build your termination strategy, you’ll want to scout your fields and verify just how much cover crop growth you have.”

When you plant your cover crop will largely impact how much growth you have. Farmers who over-seeded or planted early will see a lot more growth and will need to plan for the larger biomass in their termination plan. 

Plant size will also dictate your herbicide decisions. The bigger the plant, the higher concentration you’ll want to ensure complete coverage. If your cash crop is soybeans, Carlson suggests farmers switch to contact herbicides with warmer temperatures. If your cash crop is corn, she recommends the following: 

Cover crop less than 6”

Spray the cover and plant your corn within 5 days given that your cover crop isn’t holding much nitrogen.

Cover crop greater than 6”

Delay planting or add nitrogen in a 2×2 or 2x dribble to your planter.

2 Get Your Termination Tools Ready

An important consideration for assessing field growth is making sure your termination tools are ready to go. 

Confirm your sprayer is ready & remove your row cleaners from your planter.

  • Contracting with a customer sprayer? Make sure you’re on their list and that your fields are being prioritized.
  • Own the sprayer? Make sure it’s primed to target fields in short notice.

Get your tank mix right.

  • Read the label, and don’t use too much water. Because glyphosate has a negative charge and water (especially hard water) has a strong positive charge, the more water you have, the less herbicide you’ll have available for the cover crop.
  • Consider a water softening aid, but wait until your water is at least 99% conditioned before you add glyphosate to your tank.

3 Check the forecast

Carlson’s rule of thumb is simple: Don’t spray unless day and night time temps add up to 100℉. It needs to be warm enough to ensure the cover crop plant is actively growing and will take up that herbicide.

4 Choose brown or green

If you’re new to cover crops, Carlson recommends getting your cover crop killed a week to 10 days before they start planting corn (adding that you’ll have more flexibility if you’re planting soybeans or don’t have significant cover crop growth). She always prioritizes scouting your fields. If you’ve got less than 6” of growth, you might be able to plant successfully through the residue (plant green).

5 Prioritize and stretch your supply

When it comes to when and where to prioritize using glyphosate, Ron Geis, a Market Development Specialist for Corteva with over 37 years experience working in crop protection, recommends spraying grass cover crops as first priority, with post-emergent soybean applications as second priority. “Without glyphosate, you’re left with one mode of action to control your weeds post-emerge in soybeans which will lead to long-term problems,” he added. “Most farmers can skip the glyphosate on post-emerge corn or burndown where there is no grass.”

To stretch your glyphosate supply, Geis also suggests using the full-labeled rate for your pre-emerge herbicides. Farmers can also apply their post-emerge early to ensure that the majority of chemical hits the soil and can kill weeds while they’re still small. Adding adjuvants to the mix will also help spread glyphosate and make sure every drop gets into the plants. He also suggests saving glyphosate for field borders where 80% of weeds grow.

As for substitutions, Geis offered these alternatives for both cereal rye termination and broadleaf, that also take into account plant growth.

Cereal Rye

Option # Active Ingredient Product Height
1 Rimsulfuron BASIS, RESOLVE Up to 2”
2 Nicosulfuron ACCENT, STEADFAST Up to 3”
3 Glufosinate LIBERTY Not labeled / prior to tiller (4”)
4 Clethodim SELECT 6” (price is 2-4x ‘21)
5 Paraquat GRAMOXONE Prior to tiller (4”)
6 Others BALANCE, ATRAZINE, SHARPEN, METRIBUZIN 1-2”
7 Glyphosate N/A Translocates readily to roots

Broadleaf

Option # Active Ingredient Product Attribute
1 2,4-D n/a Cross spectrum
2 Dicamba n/a Cross spectrum
3 Stinger (corn) SURESTART, RESICORE Alfalfa, large seeded

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