Planting Date and Glyphosate Timing on Soybean

Abstract

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...