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Palmer amaranth control in grain sorghum
COURTESY PHOTO Pigweeds in sorghum field

When the aggressive nature of Palmer amaranth (pigweed) is combined with the limited post-emergence herbicide options in grain sorghum, problems often arise – even when an adequate preemergence herbicide program is used. This article highlights post-emergence herbicide options for Palmer amaranth control in grain sorghum. To see the full version of the article with use rates, recommended surfactants, and plant height restrictions, search for K-State Agronomy eUpdates, June 27th issue. Combinations of the herbicides listed here will generally improve control, and all of the options are most effective when applied to small (under 4 inches tall) pigweeds.

Atrazine can control sensitive populations of Palmer amaranth and can be combined with other herbicides to enhance effectiveness. Aim (carfentrazone) is a Group 14 herbicide that can be applied to grain sorghum between 4 inches and boot stage. It is less effective than some of the other herbicides in this article and requires good coverage for maximum effectiveness. 

2,4-D is an effective herbicide option to control Palmer amaranth. However, crop response should be expected, especially if applied in hot, humid conditions. Dicamba, at the rates used in grain sorghum (0.5 pint), may be less effective on Palmer amaranth than 2,4-D. Bromoxynil can be applied from the 3-leaf stage through boot stage. Crop response will be less with bromoxynil than other herbicides, but bromoxynil alone will not control Palmer amaranth larger than 4-leaf. Bromoxynil is a contact herbicide that is not translocated in the plant. Therefore, adequate spray coverage is needed for maximum effectiveness.  

Huskie (pyrasulfutole +bromoxynil) is most effective when mixed with atrazine (up to 1 pound). When used alone, it can be applied between 3-leaf and 30 inches and should be applied with HSOC (high surfactant oil concentrate) or AMS + NIS. Huskie will cause leaf burn, which can be greater in fields where mesotrione was applied pre-emergence. Huskie plus atrazine may be tank-mixed with phenoxy broadleaf herbicides such as 2,4-D or dicamba.

Imiflex (imazamox) can only be applied to igrowth grain sorghum and only in fields that were not sprayed preemergence. Imiflex is an ALS-inhibiting herbicide, and ALS-resistance is assumed to be widespread in Kansas. However, there is limited evidence that it may still contribute to suppression of ALS-resistant pigweeds. For susceptible Palmer amaranth plants, herbicide applications should target plants that are 3” tall or less.

Other herbicide resistant sorghum technologies are also on the market and this technology specifically targets grasses. These technologies include Inzen sorghum from Corteva with the herbicide partner Zest WDG and DoubleTeam sorghum from S&W seeds with the herbicide partner First Act. 

Additional information can be found in the 2024 Chemical Weed Control for Field Crops, Pastures, Rangeland, and Noncropland, K-State publication SRP-1176- 

The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements. 

Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at or call the Hays office, 785-628-9430.