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27 March 2019 Control of Atrazine-Resistant Palmer Amaranth (Amaranthus palmeri) in Double-Crop Grain Sorghum
Marshall M. Hay, Jeffrey J. Albers, J. Anita Dille, Dallas E. Peterson
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Double-crop grain sorghum after winter wheat harvest is a common cropping system in the southern plains region. Palmer amaranth is a troublesome weed in double-crop grain sorghum in Kansas. Populations resistant to various herbicides (e.g., atrazine, glyphosate, metsulfuron, pyrasulfotole) have made Palmer amaranth management even more difficult for producers. To evaluate control of atrazine-resistant and atrazine-susceptible Palmer amaranth in double-crop grain sorghum, we assessed 14 herbicide programs, of which 8 were PRE only and 6 were PRE followed by (fb) POST applications. Visible ratings of Palmer amaranth control were taken at 3 and 8 wk after planting (WAP) grain sorghum. PRE treatments containing very-long-chain fatty acid (VLCFA)–inhibiting herbicides provided 91% control of atrazine-resistant Palmer amaranth 3 WAP, and reduced weed density 8 WAP compared to atrazine-only PRE treatments. PRE fb POST treatments, especially those that included VLCFA-inhibiting herbicides, provided greater control (71% to 93%) of both atrazineresistant and atrazine-susceptible Palmer amaranth, respectively, at 8 WAP compared to PRE treatments alone (59% to 79%). These results demonstrated the utility of VLCFA-inhibiting herbicides applied PRE and in a layered PRE fb POST approach in controlling atrazineresistant Palmer amaranth, as well as the importance of an effective POST application following residual PRE herbicides for controlling both atrazine-resistant and atrazinesusceptible Palmer amaranth in double-crop grain sorghum.

Nomenclature: Atrazine; glyphosate; metsulfuron; pyrasulfotole; Palmer amaranth, Amaranthus palmeri S. Wats.; grain sorghum, Sorghum bicolor L.; winter wheat, Triticum aestivum L.

© Weed Science Society of America, 2019.
Marshall M. Hay, Jeffrey J. Albers, J. Anita Dille, and Dallas E. Peterson "Control of Atrazine-Resistant Palmer Amaranth (Amaranthus palmeri) in Double-Crop Grain Sorghum," Weed Technology 33(1), 115-122, (27 March 2019).
Received: 20 August 2018; Accepted: 4 November 2018; Published: 27 March 2019

Herbicide resistance
layered residual
soil-applied residual
very-long-chain fatty acid–inhibiting herbicides
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