Weed seed return as influenced by the critical weed-free period and row spacing of no-till glyphosate-resistant soybean

Seed return from later-emerging weeds is a concern in soybean management sy stems based on critical periods for weed control. This study in Ontario est imated the weed seed return to the soil surface as influenced by the durati on of weed control in soybean and soybean row spacing. Weeds emerging after the 1- to 2-trifoliate stage of soybean development did not increase the w eed seedbank population compared to the residual population in the weed-fre e control. Weed seed return was greater in 76 cm than in 38 cm or 19 cm (tw in rows) soybean row spacings.