USCP Agronomy Check


   By now, many growers have planted their grain sorghum and may be considering post weed control options. Hopefully, a pre-emergence herbicide was applied, since it will go a long way in providing successful control of many weeds. The key for successful weed control in sorghum starts with a pre-emergence program that includes a mix of a chloroacetamide herbicide with atrazine. There are several premixes on the market including Bicep II Magnum, Guardsman Max, Degree Xtra, Fultime NXT and various generic equivalents. These are all reasonably effective on annual grasses and broadleaf weeds. 
   Post-emergence control
   For post-emergence broadleaf weed control, there are several options available depending on the particular weeds present. Scout fields early for the emergence of weeds, and apply herbicides when weeds are small to prevent loss of yield from early-season competition. In addition, all post-emergence herbicides are much more effective when applied to small weeds. Once most broadleaf weeds get taller than about 4 inches, they become much more difficult to control. Atrazine plus crop oil generally will do a very good job of controlling many small broadleaf weeds, especially palmer amaranth and tall waterhemp. Although there are some areas where these weeds have become resistant to atrazine, in most fields it is still a very effective herbicide. 
   For other broadleaf weeds it may be necessary to use 2,4-D or dicamba in combination with atrazine. When using these two products, it is important to apply to grain sorghum that is less than 8 inches tall, or significant crop injury can occur. These products can be applied on sorghum up to 15 inches tall if drop nozzles are used to limit the amount of herbicide being absorbed by the sorghum leaves. 

   Starane Ulta can be used in place of 2,4-D or dicamba if kochia or morningglory species are present. Apply with a nonionic surfactant. This product has very good activity on these weeds, but is weak on pigweed. Starane Ultra is also safer on sorghum and can be broadcast-applied up to the seven-leaf stage. 
   For fields that have nutsedge, the herbicide of choice is Permit. Use with crop oil or nonionic surfactant. Permit can be applied to sorghum up to 15 inches in height. Permit will not be effective on many broadleaf weeds. If both nutsedge and broadleaf weeds are present, consider using a premix product called Yukon that contains both Permit and dicamba. 
   One of the newest products on the market for broadleaf weed control is Huskie. Although most effective on small weeds, it can be used as a rescue treatment on larger weeds if necessary. Huskie can be applied to 30-inch tall sorghum before flag leaf emergence. Temporary sorghum leaf spotting and yellowing will likely occur, but sorghum typically grows out of these injury symptoms within a few days. Control will not be as consistent or as good on large weeds, but Huskie can be an effective treatment.
   Visit the Sorghum Checkoff website at for links to various state extension weed control guides. Always read and follow label instructions, and consider regional and crop rotation restrictions when using herbicides.
 BRENT BEAN: Agronomist, United Sorghum Checkoff Program

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