Author(s)

Brittany K. Hedges, Nader Soltani, David C. Hooker, Darren E. Robinson, Peter H. Sikkema

University of Guelph, Ridgetown Campus, Ridgetown, Canada.

Waterhemp is a small-seeded, dioecious, broadleaf weed that emerges throughout the growing season. If left uncontrolled, waterhemp interference can reduce soybean yield up to 73%. Glyphosate-resistant (GR) waterhemp was first discovered in one county in Ontario in 2014; as of 2017, it has been found in two other counties. Glyphosate/dicamba-resistant soybean can be sprayed with glyphosate and/or dicamba preplant (PP), preemergence (PRE) and/or postemergence (POST). The objective of this study was to determine the control of GR waterhemp in glyphosate/dicamba-resistant soybean with PRE residual herbicides, glyphosate/dicamba applied POST or a two-pass program of a PRE residual herbicide followed by glyphosate/dicamba applied POST. At 8 weeks after application (WAA), pyroxasulfone (150 g ai ha^-1), S-metolachlor/metribuzin (1943 g ai ha^-1), pyroxasulfone/sulfentrazone (300 g ai ha^-1) and flumioxazin/pyroxasulfone (240 g ai ha^-1), applied PRE, resulted in 71%, 85%, 82% and 90% GR waterhemp control, respectively. The same PRE herbicides, followed by glyphosate/dicamba (1800 g ae ha^-1) POST, improved control to greater than 96%. This study concludes that a two-pass program of an effective soil applied residual herbicide followed by glyphosate/dicamba POST controlled GR waterhemp in glyphosate/dicamba-resistant soybean.

Waterhemp, Soybean, Glyphosate Resistance, Glyphosate, Dicamba

Hedges, B. , Soltani, N. , Hooker, D. , Robinson, D. and Sikkema, P. (2018) Control of Glyphosate-Resistant Waterhemp with Two-Pass Weed Control Strategies in Glyphosate/Dicamba-Resistant Soybean. American Journal of Plant Sciences, 9, 1424-1432. doi: 10.4236/ajps.2018.97104.