Enlist Weed Control Systems for Controlling Horseweed (Conyza canadensis) in Enlist Soybean

Aims: Evaluate glyphosate-resistant Conyza canadensis control with Enlist weed control systems that include sequential applications of burndown application prior to Enlist soybean (Glycine max (L.) Merr.) planting followed by an early postemergence application to Enlist soybean.

Study Design: Studies conducted as randomized complete block with 4 replications.

Place and Duration of Study: Twenty-one field studies were conducted between 2014 and 2015 growing seasons across soybean production areas in the United States.

Methodology: Prior to planting, burndown applications of glyphosate, glyphosate + 2,4-D choline, glufosinate, or glufosinate + 2,4-D choline were applied with and without sulfentrazone + cloransulam. At the V3 growth stage of Enlist soybean, postemergence applications of glyphosate, 2,4-D choline + glyphosate, glufosinate, 2,4-D choline + glufosinate or glyphosate + dicamba were applied according to the defined sequential program. Visual control ratings of weed control were taken at 4 weeks after each application.

Results: Conyza canadensis control at 4 weeks after the burndown application (28 DABA) was 54% for glyphosate, 97% for glyphosate + dicamba, 93% for 2,4-D choline + glyphosate, 85% for glufosinate, 92% for 2,4-D choline + glufosinate. Applying a second application of 2,4-D choline + glyphosate, 2,4-D choline + glufosinate or glyphosate + dicamba resulted in ≥95% control of Conyza canadensis 28 days after sequential application. The addition of sulfentrazone + cloransulam to the first application provided more consistent control at both observation dates.

Conclusion: Enlist E3 soybean enabled burndown applications or postemergence applications of 2,4-D choline Colex-D + glufosinate or glyphosate that provided >95% Conyza canadensis control. Residual herbicides sulfentrazone + cloransulam can be included in the burndown application to provide residual control. Early post-emergence applications of 2,4-D choline + glyphosate or glufosinate can be utilized to provide control of any surviving or newly emerged Conyza canadensis.