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1 April 2007 Planting Date and Glyphosate Timing on Soybean
Jeffrey A. Coulter, Emerson D. Nafziger
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Planting date of soybean may be one factor that affects the crop's ability to compete with weeds. Field experiments were conducted over 3 yr at two locations in Illinois to determine whether planting date affects optimal weed management strategies and the critical time of weed removal (CTWR) in glyphosate-resistant soybean. Across planting dates, a PRE application of metolachlor plus metribuzin followed by a single glyphosate application at a 10- or 20-cm weed height at Monmouth or at a 20-cm weed height at Urbana was effective at protecting yield. At Monmouth, higher yields occurred with sequential glyphosate applications than with a single application in the early planting in 2 yr when weeds were removed at a height of 10 cm. Across planting dates, highest yields at Monmouth occurred with a single glyphosate application when weeds were 20 to 30 cm tall. At Urbana, the CTWR was not affected by planting date and occurred between 176 and 290 growing-degree days (GDD) after planting, corresponding to the V1 to V2 stage of soybean development and a weed height of 11 to 19 cm. Applying glyphosate near the CTWR at Urbana (10-cm weed height) required a sequential application to prevent yield loss with early and middle planting dates in 1 of 3 yr. Overall, planting date did not affect optimal weed management strategies at either location.

Nomenclature: Glyphosate; metolachlor; metribuzin; paraquat; soybean, Glycine max (L.) Merr.

Jeffrey A. Coulter and Emerson D. Nafziger "Planting Date and Glyphosate Timing on Soybean," Weed Technology 21(2), 359-366, (1 April 2007).
Received: 6 February 2006; Accepted: 1 August 2006; Published: 1 April 2007

Herbicide-resistant crops
Weed interference
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