By Larry Steckel, Extension Weed Specialist
A wet and mostly cold March has us well behind the pace for burndown. As soon as the weather permits corn planting will take priority followed by burndown for grain sorghum and early planted soybean.
What should my burndown strategy be for those crops with planting time upon us? In corn, a burndown at planting of Gramoxone + atrazine can be an effective choice. Another good option would be glyphosate + Verdict or Sharpen which should be both effective and allow for flexibility if the corn stand is lost and then replanted to soybean. The bottom line in corn is that even if some marestail recovers from the burndown application herbicides like Halex GT or Capreno spiked with either atrazine or Status have been very effective controlling large marestail in our research.
In the case of grain sorghum, please be aware that dicamba and 2,4-D can be used pre plant for burndown but not pre emergence. The reason for this is that rain can wash those herbicides into the planting slot and harm stand establishment.
In grain sorghum, a burndown at planting of Gramoxone can be an effective choice. Another good option would be glyphosate + Verdict or Sharpen which should be both effective and allow for flexibility if the grain sorghum stand is lost and then replanted to soybean. Marestail that survives burndown can be fairly easily controlled with Huskie spiked with atrazine.
Please note that herbicides we commonly use in corn like Princep and Status are not labeled in grain sorghum due to crop injury potential. Even atrazine should be used with caution pre emergence as some stand establishment problems have been documented. Post emergence atrazine applications are fine.
In the case of corn and grain sorghum it will be more critical to control Italian ryegrass than marestail before the crop emerges. In both crops there is no herbicide that can be applied post emergence that will control ryegrass. Sequential applications of Gramoxone separated by a week to 10 days can be an effective ryegrass option pre crop emergence. In corn Select Max can be applied 6 days before planting at 6 oz/A and when tankmixed with glyphosate has proven to be fairly effective. The plant back to grain sorghum from a Select Max application is 30 days.
In some cases where the plan is to plant some fields to soybean in early April, dicamba, which has been our “go to” glyphosate-resistant horseweed herbicide is no longer an option. Sharpen or Verdict would be a good new “go to” in these situations for soybean burndown.
Close to Soybean Planting Burndown Options
Sharpen 1 oz/A or Verdict 5 oz/A + Roundup PM 32 ozs/A
Management Considerations
- Sharpen at rate of 1 oz/A can be applied right up to planting.
- For large horseweed (>4”) consider increasing Sharpen rate to 1.5 oz/A or Verdict to 7.5 ozs/A and/or 1 pt of 2,4-D. – Plant back to soybean for higher rates of Sharpen or Verdict is 14 days; Plant back for soybean is 7 days after a pint of 2,4-D.
Clarity 8 ozs/A + Roundup PM 32 ozs/A
Management Considerations
- Clarity rates of 8 ozs/A can be applied up to 14 days before planting and 1” of rainfall to avoid crop injury.
Gramoxone Inteon 40 to 48 ozs/A + 0.25% NIS + Sencor 4 ozs/A or Canopy
4 to 6 ozs/A or Boundary 20 ozs/A.
Management Considerations
- This application can be applied right up to planting.
- Gramoxone Inteon rates below 40 ozs/A will not provide as consistent control of horseweed as higher rates.
- For larger horseweed (>6”) use 48 ozs/A of Gramoxone Inteon.
FirstRate 0.3 to 0.4 oz/A + Roundup PM 32oz/A
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