Predictions are that significantly more acres will be planted to LibertyLink soybeans this spring. Weed scientists believe one key to success with a LibertyLink system is to include effective residual herbicides to tackle the toughest weeds.

Bill Johnson and Travis Legleiter, Purdue University weed control specialists, and Mark Loux, Johnson’s counterpart at Ohio State University, prepared recommendations for how to achieve effective weed control in LibertyLink soybeans. They focused on the best choices for residual herbicides in a LibertyLink system, depending upon the weeds in your mix.

“Residual herbicides reduce weed densities, slow weed emergence and provide flexibility in the postemergence application window,” Johnson says. “A residual herbicide premix which targets troublesome broadleaves and suppresses grasses is most ideal.”

Suggested options
Here are options for residual premixes to be used in LibertyLink systems for tough weeds. Recommendations were prepared by the trio of weed control experts.

• Marestail. One option is Authority First/XL/Assist/Maxx, Envive/Enlite, Fierce/FierceXLT, Rowel FX, Sonic, Spartan, Surveil, Trivence or Valor/Valor XLT.

A second option would be metribuzin-containing products or mixtures that provide at least 0.38 to 0.5 pound of active ingredient per acre.

If you have dense marestail infestations, the weed scientists suggest a third option. Opt for an Authority- or Valor-based premix with metribuzin if you’re after top control in this situation.

• Waterhemp or Palmer amaranth. The residual program rated best by these experts to accompany a postemergent application of Liberty in LibertyLink soybeans includes: BroadAxe SC, Fierce/Fierce XLT or Trivence. Residual herbicides the trio rates as good on these weeds include: Anthem, Authority Assist/ First/MTZ/Maxx/XL, Envive/Enlite, Rowel FX, Sonic, Surveil, Valor/Valor XLT or Zidua.

They rate the following residual products as providing fair control: Outlook, Optill Pro, pendimethalin, Prefix, S-metolachlor, Warrant or Warrant Ultra.

• Lambsquarters. For residual help on this tough weed in a LibertyLink system, Johnson, Legleiter and Loux say almost any residual herbicide will work. However, herbicides with the active ingredient metolachlor tend to be somewhat weak on lambsquarters.

• Giant ragweed. Residual herbicides that could be used in the LibertyLink system include: Authority First/Maxx/XL, Canopy/Cloak DF or EX, Envite/Enlite, Fierce XLT, FirstRate, Rowel FX, Scepter, Sonic, Surveil, Trivence or Valor XLT. However, if the ragweed population is ALS-resistant, performance of residual herbicides will be less satisfactory.

Special note on grasses
Glufosinate can be weak on some annual grasses, the experts note. These include barnyardgrass, crabgrass and yellow foxtail. If the residual herbicides you choose aren’t good on these species, they suggest considering adding a post grass herbicide when you apply glufosinate postemergence. Post grass herbicide options include Select, Assure II, Fusilade, Fusion, Poast and other similar products.

Special note on pigweeds
Adding S-metolachlor, Outlook, Warrant or Zidua  to the first postemergence application provides an extra layer of residuals to control later-emerging grasses and small-seeded broadleaves, including Palmer amaranth and waterhemp. This also provides extra insurance on control of pigweeds, and may extend the window for a second application of glufosinate postemergence, or even provide enough control that the second application isn’t needed.