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13 August 2019 Integrated pigweed (Amaranthus spp.) management in glufosinate-resistant soybean with a cover crop, narrow row widths, row-crop cultivation, and herbicide program
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Successful pigweed management requires an integrated strategy to delay the development of resistance to any single control tactic. Field trials were implemented during 2017 and 2018 in three counties in Kansas on dryland (limited rainfall, nonirrigated), glufosinate-resistant soybean. The objective was to assess pigweed control with combinations of a winter wheat cover crop (CC), three soybean row widths (76, 38, and 19 cm), row-crop cultivation 2.5 weeks after planting (WAP), and an herbicide program to develop integrated pigweed management recommendations. All combinations of the four components were assessed by 16 treatments. All treatments with the herbicide program resulted in excellent (>97%) pigweed control and were analyzed separately from the other components. Treatments containing row-crop cultivation reduced pigweed density and biomass 3 and 8 WAP in all locations compared with the 76-cm row width plus no CC treatment. CC impacts were mixed. In Riley County, Palmer amaranth density and biomass were reduced; in Reno County, no additional Palmer amaranth control was observed; in Franklin County, the CC had greater waterhemp density and biomass compared with the treatments containing no CC. Narrow row widths achieved the most consistent results of all cultural components when data were pooled across locations: Decreasing row widths from 76 to 38 cm resulted in a 23% reduction in pigweed biomass 8 WAP and decreasing row width from 38 to 19 cm achieved a 15% reduction. Row-crop cultivation should be incorporated where possible as a mechanical option to manage pigweed, and narrow row widths should be used to suppress late-season pigweed growth when feasible. Inconsistent pigweed control from CC was achieved and should be given special consideration before implementation. The integral use of these components with an herbicide program as a system should be recommended to achieve the best pigweed control and reduce the risk of developing herbicide resistance.

Nomenclature: glufosinate; pigweed, Amaranthus spp., Palmer amaranth, Amaranthus palmeri S. Watson; waterhemp, Amaranthus tuberculatus (Moq.) J. D. Sauer; soybean, Glycine max (L.) Merr.; winter wheat, Triticum aestivum L.

© Weed Science Society of America, 2019.
Marshall M. Hay, J. Anita Dille, and Dallas E. Peterson "Integrated pigweed (Amaranthus spp.) management in glufosinate-resistant soybean with a cover crop, narrow row widths, row-crop cultivation, and herbicide program," Weed Technology 33(5), 710-719, (13 August 2019).
Received: 25 March 2019; Accepted: 21 June 2019; Published: 13 August 2019

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