It is “Burndown Time in Tennessee.”

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Failed glyphosate + dicamba burndown on ryegrass before corn planting in 2022

The combination of some lingering supply chain issues, most notably Sharpen and Verdict are in tight supply, with the ever-increasing presence of herbicide resistant weeds has made burndown time more of a challenge. On a positive note, glyphosate is in great supply and down in price about 40% compared to last year.

Ryegrass is of most concern, particularly before corn planting.  There are two reasons for the sketchy control we sometimes see.  First, the continued evolution of glyphosate resistance in ryegrass populations has made the most common burndown tankmix of glyphosate + dicamba very inconsistent. Second, preliminary data would suggest that dicamba is antagonizing glyphosate causing this mix to provide poor ryegrass control.  As such our recommendation has been to change the “go-to” burndown from glyphosate + dicamba to glyphosate + clethodim when grasses are the primary target.

The problem with using glyphosate + clethodim is that this burndown will miss or be weak on some broadleaf weeds, most notably glyphosate-resistant horseweed.   So, is there a herbicide that can be added to glyphosate or glyphosate + clethodim that will provide horseweed control while not sacrificing ryegrass control? There is really only one option that is in good supply that would fit the bill.

This option is Elevore, which is an auxin-mimic herbicide with a mode of action similar to 2,4-D. In our research it has provided horseweed control as good as Sharpen or Verdict. One big plus we have seen with Elevore compared to dicamba is the greatly reduced grass antagonism when mixed with glyphosate.

Another option if you can get it would be saflufenacil (trade names Sharpen or Verdict). In short, the saflufenacil tankmix with glyphosate improves grass control. If you can access Sharpen or Verdict they can be effective options in a tankmix with glyphosate + clethodim to provide control of ryegrass as well as horseweed. Please keep in mind the smaller the ryegrass the better chance of control with that tankmix. Poa control from this tankmix is also typically pretty good. Please keep in mind the plant back to cotton after Sharpen is 1 month and to Verdict is 6 months.  However, there is no waiting period to plant corn, grain sorghum or soybeans after a 1 oz/A of Sharpen or 5 oz/A of Verdict.

If the field in question is infested with just scattered horseweed a possible option would be to go with a glyphosate + clethodim burndown to take out the grasses.  Then control the horseweed in-crop with dicamba in Xtend crops or Enlist One in Enlist crops.

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