Fall Burndown Considerations for Corn and Soybeans

When harvest wraps up, you might be tempted to park the sprayer for the season — but skipping a fall burndown could cost you next spring.

Benefits of a fall burndown herbicide

Consider some of the agronomic and economic benefits from implementing a fall burndown weed-control strategy:

• Limit overwintering pests: Fall burndown helps limit pests and pathogens that would ordinarily make their homes in winter weeds.
• Reduce spring weed biomass: Avoid plentiful spring weeds that can make planting a tougher job than it needs to be.
• Curb weed competition: Give your crops a chance to develop a strong stand and produce higher yields in the upcoming growing season by pushing back on weeds that steal valuable nutrients and water.
• Find potential economic advantages: Avoid the extra expense of labor and fuel managing excess weeds at planting time, plus ensure you use fall burndown herbicide only where you need it when weather and temperature are optimal.

Now that you know some of the key advantages of a burndown herbicide, it’s time to assess best practices for timing.

Timing considerations for fall burndown herbicides

It’s best to apply a burndown herbicide when fall weeds are still actively growing. This occurs when daytime temperatures are 50 F or greater.² Aim for the window from late October to mid-November.
You can theoretically apply herbicide if temperatures are slightly cooler, say 40 F to 60 F. But weed control may be slower in those conditions since colder temperatures reduce rates of absorption and the movement of herbicides such as glyphosate and 2,4-D within plants.
If a hard freeze has occurred, review weed conditions before deciding whether to apply herbicide. You don’t want to waste herbicide (or money) in the field if it won’t function properly on weeds.

Identifying problem weeds for fall burndown herbicides

To ensure your fall burndown is as effective as possible, know which weeds are the best candidates for burndown treatment.
In late summer or fall, scout for winter annuals that have entered the rosette stage. This means the weeds appear in small clumps (they look a little bit like badges) at the soil surface.³

Next, use weed-identification apps, websites, and insights from trusted advisers and your personal experience to determine what species you’re dealing with. This will help you determine the best herbicide to use alongside other practices such as biological, cultural, crop genetics and even mechanical control methods.

Ideal conditions for burndown herbicide application

Fall burndown herbicides usually perform best when temperatures are between 60 F and 75 F at application.⁴ These conditions should remain for several hours post-application for maximum effectiveness. At temperatures lower than 60 F, the herbicide will move more slowly inside the weeds, which grow more slowly in colder conditions. The herbicide will eventually do its work, but that will become apparent more slowly than if it had been applied under optimal temperatures. So, evidence that you’ve done the job correctly will be somewhat delayed. Don’t apply glyphosate-based herbicides when temperatures are below 40 F.

One way to improve the efficacy of your herbicide is to add an adjuvant.⁵ These oil-based solutions are especially effective in drier environments with low relative humidity. They work by slowing the rate at which droplets dry, giving the herbicide more time to work its way into weed leaves.

For fall burndown applications, Clarity® herbicide is labeled for application between crops. Be sure to follow crop rotation restrictions and wait the recommended amount of time between the herbicide application and planting a specific crop.
There are no rotational restrictions if you plant these crops at least 120 days after Clarity application. If you are planting 120 days or less following an application, follow these labeled guidelines:

• For corn: Use a burndown in the fall or spring prior to planting corn. Use up to 16 ounces per acre of Clarity on soils 2.5% or greater OM or up to 8 ounces per acre on soils less than 2.5% OM.
• For soybeans: You may apply up to 16 ounces per acre prior to planting soybeans if at least 1” of rainfall has occurred and you’ve observed a waiting period of at least 28 days. If you are using 8 ounces per acre or less, you must have observed at least 1” of rainfall and a waiting period of at least 14 days.

Herbicide and tank mix strategies

Following are some general rules of thumb. For more specifics, you should always work with a trusted adviser like your regional BASF representative to determine the best burndown herbicide and fall burndown strategy.

Glyphosate

More active in warmer temperatures compared to 2,4-D, which can perform better in colder conditions.

2,4-D

A bit more active than glyphosate when conditions are below 40 degrees F. Should be tank-mixed with a residual in most cases.

Tank mixing with residuals

This can be a good option post-harvest in cooler conditions when foliar herbicide applications are generally less effective⁶.

One common fall burndown approach is to tank-mix glyphosate and 2,4-D because it generally keeps costs between $5 and $15 per acre and targets a broad spectrum of weed species.

Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative to learn more.

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Endnotes

1. Pringnitz, Brent. “Fall Burndown Treatments for Winter Annual Weeds.” Integrated Crop Management News, Iowa State University Extension and Outreach, 27 Sept. 2022, https://crops.extension.iastate.edu/cropnews/2022/09/fall-burndown-treatments-winter-annual-weeds.
2. Sprague, Christy. “Getting a Start on Weed Control in the Fall.” MSU Extension, Michigan State University, 13 Sept. 2021, https://www.canr.msu.edu/news/getting-a-start-on-weed-control-in-the-fall.
3. Peachey, Ed. “How to Use Herbicides Safely to Control Weeds on Farms.” OSU Extension Service, Oregon State University, 2018, https://extension.oregonstate.edu/pests-weeds-diseases/ipm/how-use-herbicides-safely-control-weeds-farms.
4. Klein, Robert N., and Amit Jhala. “Weather and Burndown Herbicides.” CropWatch, University of Nebraska–Lincoln, 13 Apr. 2018, https://cropwatch.unl.edu/2018/weather-and-burndown-herbicides/.
5. Hager, Aaron, Bill Johnson, and Kevin Bradley. “Adjuvants with Herbicides: When and Why They Are Needed.” Crop Protection Network, 2017, https://cropprotectionnetwork.org/publications/adjuvants-with-herbicides-when-and-why-they-are-needed.
6. Curran, Bill. “Fall Burndown of Weeds and Declining Forage Stands.” Penn State Extension, Pennsylvania State University, 14 Sept. 2017, https://extension.psu.edu/fall-burndown-of-weeds-and-declining-forage-stands.