As more farmers use vertical tillage to manage crop residues or to mellow the seedbed prior to planting (especially soybeans), questions have arisen about possible impacts of using these types of tillage operations in combination with certain soybean herbicides.

The PPO herbicides (Group 14) in particular are drawing attention in these discussions. The soil applied PPO’s include flumioxazin (Valor SX, Valor XLT, and Envive); sulfentrazone (the Authority family lineup and Spartan), fomesafen (Prefix, Reflex); and saflufenacil (Sharpen, Verdict, Optill).

In general, if a vertical tillage operation is completed prior to the PPO herbicide application, residual weed control will typically not be negatively affected. However, if the PPO herbicide was included in a burndown application before the vertical tillage operation then weed control could be compromised.

In particular, flumioxazin and saflufenacil-containing herbicides can be affected the most. In this case, any tillage after herbicide application disrupts the uniform layer of herbicide potentially causing weed escapes or patchy weed control.

Even though sulfentrazone and fomesafen are labeled for preplant incorporation applications, most vertical tillage implements don’t provide enough mixing action to thoroughly incorporate the herbicide into the soil.

It seems logical to us that streaking or poor weed control may result from any residual herbicide application that is followed up closely with vertical tillage.

If vertical tillage must be performed as close to planting as possible then another option to consider would be to spray the burndown herbicides (e.g., glyphosate, paraquat, 2,4-D) first, then conduct the tillage procedure and then apply the PPO herbicide near planting to allow more residual effects of the PPO herbicide longer into the season.

On a side note, keep in mind that vertical tillage equipment is not designed to provide weed control, so don’t be surprised if weeds are still evident after running this tool over the field.