How a Burndown Herbicide Approach Can Help Production

A successful crop begins long before the seed is planted. With this year’s crop in the bin and a new year on the horizon, now is the time to develop strategies that can help you accomplish your production goals. One key protocol to keep in your production arsenal is a spring burndown herbicide application.  

📸: @chas53 via Canva/Depicting spring burndown herbicide application. 

What is a burndown herbicide? 

An effective weed control program includes season-long control. Burndown herbicides can provide powerful, effective weed control to prepare for planting. Additionally, burndown herbicides can decrease the weed seed bank during the growing season, helping to jump-start weed management early in the crop year. 

What does a burndown herbicide do?  

Spring can be a tricky time for growers. Early spring weeds can quickly get out of control as temperatures warm and days grow longer. Stealing soil moisture and tying up valuable nutrients, troublesome species like marestail and giant ragweed can make planting difficult. By starting the growing season with a weed control program that includes pre-plant burndown herbicide application, residual weed control can be more successful. Effective weed management prior to planting can help growers create a clean seedbed and reduce weed seedbank all season long.   

Benefits of burndown applications  

Economics alone tell growers that the fewer trips made across a field, the better. Still, waiting until just before planting, and including burndown along with residual herbicide application, has a number of benefits for growers. Consider these: 

• Stepped-up weed control: A few warm days are all the motivation weeds need to become a real nuisance as planting time nears. As weeds grow, they become harder to control, and herbicides become less effective against them. Some herbicides are more effective on smaller weeds than on larger ones. The common burndown herbicide paraquat, for example, can be much more effective at controlling marestail (horseweed) when the weed is less than 3” tall than after the species has grown larger. Cool or cold conditions slow plant metabolism, making it take longer for herbicides to degrade in plants. Warm conditions allow crop plants to escape herbicide injury because of rapid degradation.  

When prevent-plant situations caused by wet weather lead to delayed planting and harvest, making fall burndown impossible, winter annuals and early-emerging spring weeds become more prevalent and difficult to control. In these instances, a spring burndown herbicide application can benefit no-till operations, providing effective management of difficult-to-control emerged weeds. 

📸: @addman8 via Canva/Highlighting early-season weeds in field.

Burndown herbicide application results are best when weeds are small and actively growing.  

• Improved spray coverage in pre-plant burndown herbicide: Weeds that become too large are challenging to control because herbicide droplets can be intercepted by upper leaves. Thus, the herbicide might never reach the lower leaves, decreasing the likelihood of injury that will eventually kill that weed. Using a contact herbicide like Sharpen® herbicide can help growers achieve better spray coverage in preplant burndown herbicide applications as more spray droplets reach multiple leaf surfaces.  

• Influenced herbicide resistance: Glyphosate is widely used in spring burndown herbicide applications. Certain clay-based herbicide formulations can cause glyphosate resistance, making the herbicide less effective in weed control. To capture the greatest weed control benefit from spring burndown, avoid using clay-based herbicide formulations. 

• Longer-lasting residual: Residual, pre-emergence, herbicides protect the crop with early, effective, and lasting weed control. Typically, residual herbicides can provide successful control for approximately four to five weeks. When herbicide is applied too early, growers run the risk of only two weeks or so of weed control. Then the herbicide begins to dissipate and weeds start to regrow and challenge the crop. Length of residual control becomes even more important for growers when stubborn weeds like Palmer amaranth, waterhemp, and marestail are present. Growers often receive greater weed control value when residual products such as Zidua® PRO herbicide are applied at planting. Including a residual herbicide at spring burndown reduces the need for post-emergence herbicide applications. Spring burndown applications that include a residual herbicide also protect against early-season weed competition at a time when weather or busy schedules might prohibit post-emergent application.  

In strip or vertical tillage situations, burndown or residual herbicide application should follow tillage. Delaying the herbicide application for a time can be beneficial. This allows weeds disturbed by the tillage to recover and be better controlled with a later residual herbicide application.  

Because vertical tillage does not effectively remove all of the weeds in a field, making two herbicide applications can help avoid problems with burndown activity and residual herbicide distribution.  

If burndown/residual herbicide application occurs before strip or vertical tillage, it should take place far enough in advance of tillage for substantial rain to occur and move the herbicide into the soil profile. This can reduce the negative effect vertical tillage has on herbicide distribution. 

• Greater burndown herbicide options: It’s common for herbicide application rates to be too low for effective control. Reduced rates on certain burndown herbicides allow for the crop to be planted sooner. Using higher rates of some herbicides can provide a more direct approach to controlling early-season weeds, especially marestail. The key is knowing what weeds are the most troublesome to your operation and understanding how preplant burndown herbicide application can help you achieve a successful, profitable crop.  

 📸: @Jevtic via Canva/Featuring containers of herbicide in a soybean field.

How to choose the best burndown herbicide 

Burndown herbicide selection isn’t as simple as buying the first one you come across on the farm store shelf. Understanding what weeds are present in your fields, as well as knowing planting restrictions and how to time application with your planting schedule, are all key. Additionally, you must have a grasp on the need for residual control as well as the compatibility the herbicide might have with the crop varieties you’ve chosen. Here are some more details on how these criteria can help you choose the burndown herbicide that best meets your farm's needs.  

Weed species 

Consider a burndown herbicide with different modes of action. By applying two herbicides with unique chemistries, you increase the range of weed control. Some pre-emergence herbicides target broadleaf weeds, while others provide grass-weed control. You might need to vary the combination of burndown herbicides across a field depending on the weed species present. Choosing a single burndown herbicide could select for weeds resistant to the herbicide applied.  

Planting restrictions 

Reading the herbicide label prior to application is especially important when plantback restrictions might be required. For example, 2,4-D and dicamba have a long history of use in burndown programs because of the effectiveness and affordability of the herbicide combination. However, the mix includes drawbacks: Plantback restrictions typically range from 7 to 30 days depending on the application rate. Be sure to schedule planting accordingly to comply with label guidelines. 

Planting schedule 

Some spring burndown herbicides can be used without any planting delays. BASF’s Sharpen® burndown herbicide allows for an earlier planting window while delivering broad-spectrum control of broadleaf weeds.  

Soybean varieties that are dicamba-tolerant and 2,4-D choline-tolerant allow the use of approved herbicide formulations for preplant burndown without delay in planting. By using the full labeled rate and a full load of suggested adjuvants, control failures can be avoided, especially when weeds become stressed by cold conditions and are larger when the herbicide is applied.  

The nonselective, widely used burndown herbicide paraquat can provide quick and effective control of a variety of weed species. However, it must be applied in favorable weather conditions for the best results. Because paraquat is most effective when thoroughly applied, spraying in windy conditions should be avoided.    

Residual control needs 

Using a burndown herbicide that offers good residual control can help you manage weeds for a longer period of time. Herbicides such as atrazine, metribuzin, and flumioxazin are valuable components to control early-emerging species, including common lambsquarter and giant ragweed, before planting soybeans.  

Consider using Verdict® herbicide enhanced pre-emergence herbicide from BASF to provide a strong residual foundation for corn and soybeans. Its burndown capabilities help it provide consistent weed control throughout the season. Verdict can be used preplant without restrictions.  

Crop compatibility 

Understanding how a burndown herbicide might affect the crop planned for your field is essential to helping maximize its production potential. Herbicides containing metribuzin have a narrow margin of crop tolerance. With proper soil testing and by following herbicide rate recommendations, you can help ensure crop and herbicide compatibility. Some products also come with crop rotation restrictions, so a thorough review of product labels and application rates can help you avoid damaging the crop. 

Options to combat herbicide resistance in crop production 

Herbicide resistance has become a recurring issue for growers in recent years. Crop rotation can be an effective management strategy to combat herbicide resistance, but varying herbicide chemistries are also necessary to maximize weed control at burndown application.  

Marestail has developed resistance to glyphosate and ALS-inhibitor herbicides. As a result, glyphosate and ALS-inhibitor herbicides are not recommended for sole use in burndown programs. However, adding dicamba, 2,4-D, or Sharpen® herbicide can provide consistent marestail control while also managing other winter annuals.  

An effective spring burndown program to control marestail might also include adding atrazine or metribuzin to 2,4-D.  

📸: @Jevtic via Canva/Highlighting early-season weeds in field.

Considerations for burndown herbicide application 

Rainy days. Rising and falling temperatures. Weather conditions in general can have a great impact on spring burndown herbicide applications. However, weather isn’t the only factor you should consider when you’re ready to apply a spring burndown herbicide. Remember to always read and follow herbicide label instructions to maximize efficacy and control weeds. Keep in mind the following criteria before herbicide application begins:  

Temperature 

Herbicides tend to lose effectiveness in cold temperatures. Daily high temperatures should be in the mid- to upper-50s prior to the day of application and three to four days after application. Low temperatures at this time should not fall below freezing for the best herbicide results. Even in these conditions, it could take up to four weeks following application before visual levels of control appear, depending on the herbicide mixture. Thus, be cautious on follow-up applications.  

​​Glyphosate typically performs well under a wide range of temperatures, with best performance occurring when the temperature is between 60°F and 7°F at application and remains there for a few hours afterward. ​ 

In temperatures below 60°F, weed growth slows, resulting in slower herbicide conversion to the plant. 

Weather conditions 

In farming, you’re at the mercy of Mother Nature during all stages of the growing season. Prior to herbicide application, it’s a good idea to monitor weather conditions. The efficacy of burndown herbicides can be directly affected by wind and rainfall. Check herbicide labels for suggestions on how much time to allow between application and subsequent rainfall to ensure full herbicide efficacy. This time is known as the rainfast period.  

Herbicides are given a rainfast rating based on good growing conditions. For example, poor conditions could require a longer wait between application and rainfall to allow for acceptable herbicide transfer within the weed before the chemical is washed off. Any amount of rainfall soon after spraying could potentially reduce weed control.     

Herbicide spray coverage 

Accurate spray coverage is essential to ensuring all weed surfaces are coated. Give consideration to spray pressure and volumes as directed by the herbicide label. Be sure to use the appropriate nozzle for the herbicide you’re applying. Speed and pressure should direct your choice of nozzle to ensure the best coverage. 

When mixing the spray solution, remember that "order" matters. You can avoid unintentional results by following the D.A.L.E.S. method. Follow this "order" when mixing products: 

• Dry products 

• AMS (ammonium sulfate) 

• Liquid and SC (suspension concentration) herbicide formulations 

• Emulsifiable concentrates 

• Surfactants  

Paying attention to detail is necessary to properly clean and calibrate the sprayer. The spray solution should be thoroughly cleaned from the sprayer before switching from one herbicide to another to avoid potential crop injury from spray residue. Improper sprayer care can cause untimely crop damage that results in problems later in the growing season.  

Timing of crop planting 

When applying a spring burndown herbicides, remember that many products only control germinated weed seeds, not emerged weeds. Most often, at least a half inch of rainfall is needed to help pre-plant herbicide transfer into the soil layer where weed seeds germinate. Monitor weather conditions prior to application. In an ideal application event, a spring burndown herbicide should be applied before rain. If rain doesn’t occur within seven days of herbicide application, field scouting should take place to determine if a postemergence herbicide will be necessary.  

Remember to allow enough time for the herbicide to act on the weeds before planting. Herbicide effectiveness might be reduced when applied too close to planting. Read how fall burndown applications result in a cleaner start in the spring. 

Herbicide application rate 

Application rates for spring burndown herbicides are based on soil type. Sandy soils, or those with a coarse texture, typically call for a lower rate than loam or clay soils. It’s also important to select a rate based on the field you’ll be spraying. Rates should then be adjusted accordingly to other fields when needed to accommodate for in-field variation. Remember, the rate has a direct impact on crop injury, subpar weed control, and injury to successive crops when misapplied.  

📸: @BanksPhotos via Canva/Featuring a sprayer applying herbicide to a corn field.

A successful, weed-free crop depends on season-long control  

Burndown herbicides play a key role in effective weed management of corn and soybean fields. Using proper burndown strategies can help set the stage for clean fields that promote crop performance and maximize yield.  

Learn more at Grow Smart® Live: 

Your herbicide retailer, university extension specialist, and regional BASF representative are available to assist with your spring burndown herbicide decisions. Learn more at Grow Smart® Live.

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Endnotes 

1. “Should Burndown Herbicide Be Applied Now,” Penn State Extension. 2023. https://extension.psu.edu/should-burndown-herbicide-be-applied-now 
2. “Burndown and Pre-emergence Herbicides for Weed Control in Corn and Soybean,” Cropwatch, University of Nebraska-Lincoln. 2020. https://cropwatch.unl.edu/2020/burndown-and-pre-emergence-herbicides-weed-control-corn-and-soybean 
3. “How Temperature and Rain Can Affect Burndown Herbicides,” Cropwatch, University of Nebraska-Lincoln. 2020. https://cropwatch.unl.edu/2018/weather-and-burndown-herbicides 
4. “Herbicide Selection for Winter Weed Burndown Amid High Prices and Product Shortages,” University of Arkansas Research and Extension. 2022. https://arkansascrops.uada.edu/posts/weeds/2022-herbicide-selection-winter-weed-burndown-prices-shortages.aspx#:~:text=Paraquat%2DBased%20System%20and%20Marestail&text=So%2C%20depending%20on%20what%20crop,paraquat%20in%20your%20burndown%20program. 
5. “Considerations for Burndown Herbicide Applications this Spring,” Iowa State University Extension. 2023. https://crops.extension.iastate.edu/blog/prashant-jha/considerations-burndown-herbicide-applications-spring 
6. “Considerations for Preemergence Herbicides,” South Dakota State University Extension. 2023. https://extension.sdstate.edu/considerations-preemergence-herbicides 
7. “Herbicide Selection at Planting for Rice and Corn,” University of Arkansas Research & Extension. https://www.uaex.uada.edu/farm-ranch/pest-management/weed/weed-science-highlights-blog/posts/herb-selection-planting.aspx 
8. “Selecting Herbicide Program,” North Carolina State University. https://soybeans.ces.ncsu.edu/selecting-herbicide-program/ 
9. “Liberty Herbicide Application Best Practices,” BASF. https://agriculture.basf.us/crop-protection/Campaigns/Your-Land-Your-Legacy-Your-Liberty/liberty-herbicide-application-best-practices.html 
10. “Weed Control for No-Till Soybeans,” BASF. https://agriculture.basf.us/crop-protection/news-events/stories-from-the-field/weed-control-for-no-till-soybeans.html 
11. “Timing of Vertical Tillage and Herbicide Applications,” Ohio State University Extension, 2016. https://agcrops.osu.edu/newsletter/corn-newsletter/timing-vertical-tillage-and-herbicide-applications 
12. “Temperature and Herbicide Application Questions,” North Dakota State University Extension. https://www.ndsu.edu/agriculture/ag-hub/ag-topics/crop-production/diseases-pests-and-weeds/weeds/temperature-and-herbicide#:~:text=Cold%20temperatures%20may%20influence%20crop,to%20degrade%20herbicides%20in%20plants. 

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