Narrow-row soybean and a cereal rye cover crop suppress glyphosate-resistant horseweed (<i>Conyza canadensis</i>)

Abstract Alternative strategies are needed for management of glyphosate-resistant (GR) horseweed in soybean. Integrating a cereal rye cover crop with soybean planted narrow rows may improve control and reduce herbicide selection pressure herbicide-resistant biotypes. Four site-years experiments were conducted Michigan to determine whether fall-planted terminated glyphosate 1 wk prior (early termination) or after (planting green) planting combination narrow-row improved GR management. At postemergence (POST) application, biomass was reduced by 71% 90% when into rye, regardless termination time, compared no across all row widths. Planting green suppressed through harvest. When applied POST (noneffective), 36% 46% lower early cover. Similarly, 19- 38-cm 48% 28%, respectively, 76-cm rows. Cereal did not affect yield pooled over 3 4 site-years; however, yielded 11% 18% higher than Soybean an effective applied. In conclusion, fall-seeded rows; the effects last throughout growing season most cases. Delaying density harvest, but site-year due increased incidence white mold. These cultural practices have positive influence on suppressing that should be part overall strategy; use is still complete season-long