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1 June 2015 Influence of Soybean Seeding Rate, Row Spacing, and Herbicide Programs on the Control of Resistant Waterhemp in Glufosinate-Resistant Soybean
John L. Schultz, D. Brenton Myers, Kevin W. Bradley
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Abstract

Field experiments were conducted in 2012 and 2013 to determine the effects of row spacing, seeding rate, and herbicide programs on multiple-resistant waterhemp control and yield in glufosinate-resistant soybean. The two herbicide programs evaluated were: (1) a PRE application of fomesafen plus S-metolachlor followed by early POST application of glufosinate plus acetochlor, referred to as the PRE followed by (fb) POST with residual (w/RES) herbicide program; and (2) an early POST followed by a late POST application of glufosinate, referred to as the two-pass POST herbicide program. Results indicate that the PRE fb POST w/RES program provides greater control of resistant waterhemp compared to the two-pass POST herbicide program. In 2012, the PRE fb POST w/RES program resulted in a 99% waterhemp density reduction and 156 kg ha−1 increase in yield compared to the 72% density reduction by the two-pass POST program. In 2013, the two-pass POST program was equally as effective on density reduction and yield as the PRE fb POST w/RES program. Waterhemp control and density reduction was always greatest with 19- and 38- compared to 76-cm rows. In 2012, the PRE fb POST w/RES program provided at least 95% control and greater than 98% density reduction across all row spacings, whereas the two-pass POST program provided 95%, 95%, and 85% control and 87%, 80%, and 50% density reduction in 19-, 38-, and 76-cm rows, respectively. Soybean seeding rate did not affect waterhemp control or density in either year. In both years, 165,000 seeds ha−1 yielded lower than the three higher seeding rates. Overall, results from these experiments indicates that the use of a PRE fb POST w/RES program, narrow-row spacing, and seeding rates of 240,000 to 315,000 seeds ha−1 or greater provides the greatest waterhemp control, density reduction, and soybean yield when multiple resistant waterhemp is present.

Nomenclature: Common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr.

John L. Schultz, D. Brenton Myers, and Kevin W. Bradley "Influence of Soybean Seeding Rate, Row Spacing, and Herbicide Programs on the Control of Resistant Waterhemp in Glufosinate-Resistant Soybean," Weed Technology 29(2), 169-176, (1 June 2015). https://doi.org/10.1614/WT-D-14-00071.1
Received: 28 June 2014; Accepted: 1 November 2014; Published: 1 June 2015
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