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Reduced and No-Till Burndown and Pre-Emergent Weed Control

Published on Monday, April 10, 2017

As I write this, it’s raining outside. We are fortunate to receive rainfall because our soil moisture content was very low across much of the state, as we experienced very little water recharge this winter. However, with the blessing of soil moisture comes the frustration of having time to adequately prepare our ground for planting. In reduced and no-till systems, we rely on burndown chemical applications to clean our fields of weeds. The forecast indicates that we may experience rainfall at relatively consistent intervals in the near future. Frequent rainfall events, cooler temperatures, and poor drying conditions all make it difficult to get things done.

Additionally, the fall and winter conditions we experienced were mild, favoring tremendous growth of winter annual, and now, emerging summer annual weeds. Many fields going to corn and most fields going to soybeans have not had burndown chemistry applied due to saturated soil conditions and some of our fields are getting wooly! We may experience narrow windows to get both our planting and chemical application operations completed. With that said, I wanted to share a few thoughts with respect to burndown and pre-emergent weed control.

General Principles for Current Conditions

  1. Scout your fields. You need to know what weeds you have and what you are trying to control in a burndown operation.
    1. Look for spatial “hot spots.”
    2. Identify species, weed height, and growth stages.
    3. Determine if marestail (horseweed) or any perennial grasses are present and need to be controlled.
  2. Plan to apply a residual chemistry with your burndown and “bridge” or overlap residuals with an early post-emergent application.
    1. Bridging residuals between burndown and post-emergent applications is your best bet to controlling weeds.
    2. This process is the only way to effectively fight resistant weeds.
  3. Use multiple modes and sites of action when selecting chemistries.
  4. Practice timeliness as much as conditions allow. Weed control is a higher priority than planting in reduced and no-till systems. Controlling weeds when they are small, or before they emerge, is the best way to achieve your objectives. At this stage of the game, patience in planting will not hurt your yield potential. Poor weed control, however, will reduce yield.
  5. Read, understand and follow manufacturer labels for the chemicals you are applying. They are federal laws and have been written to optimize chemistry performance.
    1. Select the correct nozzles for the type of burndown chemistry you are applying, either contact or systemic. Contact chemicals such as Gramoxone® and glufosinate require coverage of weed growing points. Systemic chemicals like glyphosate require plant uptake and translocation.
    2. Understand the potential and control measures for off-target movements such as drift and volatilization, as well as the setback requirements, planting intervals, and tank cleanout procedures.
    3. Review and understand tank mix partners like residuals.
    4. Consult university efficacy ratings for various burndown chemistries with respect to the weed spectrum you are fighting. A fantastic resource I consult frequently is the 2015 Missouri Pest Management Guide: Corn, Grain Sorghum, Soybean, Winter Wheat, Rice, and Cotton. (http://extension.missouri.edu/p/M171)
  6. Accept that there may be increased costs to effectively control large and/or resistant weeds. But remember that it will cost you more in the long run if your weeds are not controlled. The long-term cost to control weeds increases significantly if resistant weed populations continue to grow.  
  7. Apply burndown chemistry when daytime temperatures are greater than 55°F and nighttime temperatures are above freezing. Typically, burndown chemistries are much more effective when the weeds are actively growing.

Lessons We Have Learned

  1. Resistant weeds, especially marestail (horseweed), are the wildcards that impact what chemistry you should apply. This is why it’s so important to scout your fields.
    1. In a typical “glyphosate, 2,4-D burndown program”, the 2,4-D has to do all the work on resistant weeds.
    2. Replace a more effective site of action chemistry for glyphosate. These options include:
      1. Applying 28 to 32 oz. of glufosinate (Liberty®, Group 10). This burndown option works much better if weeds are small (less than 4 in.) and if a fall residual was applied.
      2. Utilizing 2 to 4 pt. of paraquat (Gramoxone, Group 22).
      3. Adding 1 to 2 oz. saflufenacil (Sharpen®, Group 14) or 2 to 6 oz. of metribuzin (Group 5) to your burndown if you plan to continue using glyphosate.

Please note, Gramoxone, UAN, and metribuzin all have a tremendous “synergy” in the tank, meaning they work together well and enhance overall effectiveness of a burndown ahead of soybeans. Gramoxone, UAN and atrazine have the same synergy when applied ahead of corn. Increase the UAN rate and add some ammonium thiosulfate and you will have a nice burndown that will control resistant marestail and give you a pre-plant nitrogen starter ahead of corn or soybeans.

  1. If using glyphosate, increase the active ingredient rate to 1.12 lb./A. to control larger, non-resistant weeds or perennial grasses.
  2. When using 2,4-D, use the “ester” formulation as it is more effective in cooler weather.
    1. There is a seven-day, pre-plant interval to plant soybeans.
    2. If planting corn, make sure your corn is planted at least 2 in. deep and do not apply 2,4-D over an open planter slot.
    3. For dicamba-tolerant soybeans, the supplemental federal label allows application of dicamba, an alternative plant growth regulator to 2,4-D, in your burndown up to planting with no planting interval restriction.
  3. Add a pre-emergent residual chemistry to your burndown and “bridge” to another residual with your early, post-emergent application.
    1. My recommended approach for corn:
      1. Bridge your Group 5 (atrazine and metribuzin) and Group 15 (s-metolachlor or acetochlor) chemistries in your burndown to a Group 27 (mesotrione or topramezone) in your early, post-emergence application.
      2. Split the Group 5 atrazine application between your burndown and early post.
    1. My recommended approach for soybeans:
      1. Bridge your Group 14 (sulfentrazone or flumioxaxin) and/or a labeled Group 5 such as metribuzin or a Group 15 (metolachlor or dimethenamid-P) chemistry in your burndown to a newer site-of action Group 15 such as pyroxasulfone in your early, post-emergent application.

Mike Effertz, one of Beck’s local dealers located south of Kansas City, shared something with me that his late father said in one of their crop planning meetings years ago. While sitting at a conference table with attention spans waning as everyone wanted to be out in the field, his father Tom Effertz said, “if we get it wrong, we are going to get it wrong in here at this table. We are not going to get it wrong out there.” I love it! So make sure you plan to effectively control your weeds in less than ideal application conditions.

As always, feel free to contact your local seed advisor or field agronomist for help as you develop your burndown and residual weed control strategy.

 

 

 

 

 

 

 

 

Sharpen® is a registered trademark of BASF. Gramoxone® is a registered trademark of Syngenta. Liberty® is a registered trademark of Bayer.

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Author: David Hughes

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