Abstract
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.
Highlights
Glyphosate is a 5-enolypyruvalshikimate 3-phosphate synthase (EPSPS) inhibitor that provides broad-spectrum weed control [1]
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
Glyphosate/dicamba (1800 g ae ha−1) applied early POST (EPOST), controlled GR waterhemp by 70%, which was less than the PRE herbicides used alone (Table 2)
Summary
Glyphosate is a 5-enolypyruvalshikimate 3-phosphate synthase (EPSPS) inhibitor that provides broad-spectrum weed control [1]. The weed species resistant to glyphosate in Ontario are waterhemp [(Amaranthus tuberculatus (Moq.) Sauer var. All waterhemp populations surveyed in Ontario are resistant to Group 2 herbicides [acetolactate synthase (ALS) inhibitors], and frequently to Group 5 herbicides [photosystem II (PSII) inhibitors]; populations with multiple-sites of resistance decrease the number of herbicides available for controlling this weed species [5] [6] [7]. Herbicide resistance to five sites-of-action in one waterhemp biotype has been confirmed [3]. This limits the efficacious herbicides for waterhemp control in some populations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
