There will likely be more soybean acres in Tennessee in 2022 compared with last year. As such it will be more difficult to get POST applications applied timely. This is yet another reason overlapping residual herbicides for Palmer amaranth control will be essential in 2022. Our most recent greenhouse screens clearly show that some Palmer amaranth populations have evolved even higher dicamba resistance. This is a second reason overlapping residuals will be important. Finally, the lack of Liberty supply greatly limits the last best option to remove Palmer amaranth in-crop that is dicamba-resistant. As such, how do we best utilize overlapping residuals for Palmer control? Below are some thoughts based on our research:
Pre-Plant Options:
Option 1. Verdict 5 to 7.5 oz + Glyphosate 32 oz or Clethodim 16 oz
Advantages: Good residual control of pigweed and grasses. Provides two modes of action that are mostly effective on Palmer amaranth. Probability for soybean injury very low.
Considerations: A little more expensive than some other options. Verdict 7.5 oz rate can be applied no closer to planting than 14 days.
Option 2. Pre-Plant up to 14 days Valor 2 oz + Glyphosate 32 oz or Clethodim 16 oz. Add dicamba or Elevore if horseweed is present.
Advantages: Good residual control of pigweed. More economical than other options. Probability for soybean injury very low.
Considerations: Poor grass residual control.
PRE-Emerge Options:
Option 1. (S-Metolachlor based products) Authority Elite 24 oz or Boundary 28 oz or Prefix 40 oz or etc. + Gramoxone SL 3.0 at 32 oz
Advantages: Good residual control of pigweed and grasses. Provides two modes of action that are mostly effective on Palmer amaranth. Probability for soybean injury very low.
Considerations: Residual vine, prickly sida and copperleaf control is poor.
Option 2. (Pyroxasulfone based products) Authority Edge 7 oz or Zidua Pro 6 oz or Fierce 3 oz + Gramoxone 32 oz
Advantages: Provides multiple modes of action that are all at least mostly effective on Palmer amaranth. Good grass residual control. Better vine control than some other options. Probability for soybean injury low.
Considerations: Residual prickly sida and copperleaf control is poor.
Option 3. (Metribuzin based products) Authority MTZ 16 oz, Trivence 9 oz or Zidua Pro 6 oz etc. + Gramoxone SL 3.0 at 32 oz
Advantages: Provides multiple modes of action that are mostly effective on Palmer amaranth. Good grass residual control. Better vine control than some other options. Probability for soybean injury low.
Considerations: Residual prickly sida and copperleaf control is fair. Cotton plant back from Zidua Pro is 18 months.
Residual Post Options:
Prefix 36 oz, Warrant Ultra 60 oz, Anthem Maxx or Zidua SC 3.25 oz
