Sorghum Herbicide Options and Other Considerations

By Dwight Lingenfelter

For various reasons sorghum is starting to catch on here in the state. Some grow it as an emergency forage if initial corn crop fails, others are growing it in areas to deter crop damage from large deer populations, while others produce it for bird seed or other utilities. Whatever the reason, weed control is necessary in ensure good crop yield and herbicides provide an effective means. There are several common herbicides that can be used in sorghum such as atrazine, s-metolachlor (Dual II Magnum, Bicep II Magnum, Acuron, Lexar, Halex GT, etc.), acetochlor (Warrant, Degree Xtra, Fultime NXT, etc.), dimethenamid (Outlook, Verdict), mesotrione (Callisto, Coyote, Lexar, etc.), other products such as Clarity/dicamba, 2,4-D, Permit, Peak, Huskie, Maestro, Facet L, Yukon, as well as a few other herbicides. However, not all of these are labeled for both grain and forage (forage sorghum, sudangrass, or sorghum-sudangrass hybrids) sorghum types. In some cases, herbicide labels can be difficult to interpret as to what sorghum type for which it is labeled. All of them are labeled for use in grain types, however, only preemergence products like atrazine, Bicep II Magnum, Dual II Magnum and Warrant have forage labels.

Also, make sure that the sorghum seed is treated with a seed safener (such as Concep, Screen, etc.) before planting if using a Group 15 herbicide. As for POST herbicides, Clarity/dicamba, Huskie, Maestro, Peak, and Starane Ultra are the main choices for broadleaf weeds. Unfortunately, none of these POST herbicides control weedy grasses in-crop. That is why the newer sorghum varieties such as DoubleTeam (w/FirstAct herbicide) and igrowth (w/ImiFlex) are now on the market to help with postemergence grass control.

Planting sorghum or other crops after corn crop failure

If farmers are thinking about abandoning the current crop and planting an emergency forage crop, here are a few things to consider. Herbicide labels restrict when rotational crops such as sorghum, winter wheat or spring oats may be planted. Recrop restrictions may be based on either potential crop injury from herbicide residues in soil or the potential for illegal pesticide residues in the rotational crop. Rotation restrictions range from none to at least 26 months, so be sure to check a current herbicide label or other reliable information source before planting a rotational crop this late spring or summer.  Most atrazine containing treatments have at least a 10-month restriction before planting small grains.  Forage sorghum or sorghum-sudangrass may be better alternatives for atrazine-treated corn fields.  Although some products like Acuron, Corvus, and TriVolt allow wheat to be planted after 4 months but sorghum cannot be planted for at least 10 months or more. However, products like Bicep II Magnum (or similar products) allow any kind of sorghum to be planted immediately if corn crop fails, whereas Lumax, Lexar, and Verdict allow only grain sorghum (not forage varieties) to be planted. Acetochlor-containing products (Degree, Harness Xtra, Surpass NXT, FulTime NXT, Keystone NXT, Warrant, others) vary depending on the product, some allow immediate planting of any sorghum while others restrict the type or planting until next season. Make sure to consult the specific product label to determine if sorghum or other crops can be planted after a failed corn crop.