Michigan State University’s experiences managing glyphosate-resistant waterhemp in sugarbeet.
Glyphosate-resistant waterhemp is quickly becoming one of the most difficult weeds to manage in sugarbeet. Extended emergence, rapid growth rates, and the lack of postemergence herbicide options necessitate the use of creative options to manage waterhemp. Over the past six years we have examined various strategies and tested various herbicides for waterhemp control and sugarbeet tolerance. Acifluorfen (Ultra Blazer), phenmedipham (Spin-Aid), phenmedipham + desmedipham (Betamix), and the residual herbicides metamitron, ethofumesate and several Group 15 herbicides have all been components of this research. To date, the most consistent waterhemp control includes the use of a preemergence herbicide either ethofumesate (1.12 kg ha-1) or s-metolachlor (0.53 kg ha-1) followed by one of the overlapping herbicide programs of two applications of: 1) s-metolachlor (Dual Magnum) at 1.06 kg ha-1, 2) acetochlor (Warrant) at 1.26 kg ha-1, or 3) dimethenamid-P (Outlook) at 0.56 kg ha-1 applied at 2- and 6-8 leaf sugarbeet. In most cases, these programs also did not significantly influence sugarbeet yield. It is important to remember that the residual herbicide will not control emerged waterhemp. This is where understanding the time of waterhemp emergence in relation to sugarbeet planting is important. Most of Michigan’s waterhemp populations start to emerge the 3rd or 4th week of May. The first application of a residual herbicide would need to be applied prior to waterhemp emergence. If sugarbeets are planted later, the use of a preemergence herbicide would be needed.