What the research measured
The cited Iowa State summary of 2015–19 trials reported that pyroxasulfone alone never fell below 88% waterhemp control at three weeks, while S-metolachlor, dimethenamid-P and acetochlor gave 82% or more half the time but fell below 50% at worst and flumioxazin fell below 60% in one of five years. Purdue’s multi-year screening put Spartan, Valor, Outlook, Zidua and Warrant at 90% or greater at 28 days and metribuzin or Prowl in the mid-70s. In Minnesota’s 2015 trial a single PRE held 62 to 81% control by late September against 90 to 95% for a layered program, with a 10-bushel average yield difference.
Iowa State’s five-year PRE screening summary and 2021 program comparison, Purdue’s multi-year residual screening at 28 days, one replicated Minnesota layered-residual trial (2015) and one Ohio on-farm trial (2017). All are percent-control ratings; only Minnesota reports yield.5 independent sources.What it is. A soil-applied residual herbicide, a Group 14 (flumioxazin, sulfentrazone), Group 15 (S-metolachlor, acetochlor, dimethenamid, pyroxasulfone) or Group 5 (metribuzin) active or a premix, sprayed at or just before soybean planting so waterhemp seedlings die as they germinate. Because waterhemp emerges from May into August, the PRE is usually followed by a postemergence pass that adds a second residual, the “layered” program.
Study conditions and limitations
- Residual length is short for some actives: Purdue found metribuzin very active for two to three weeks, Prowl at 70 to 80% for four to six weeks and Sharpen at 1 oz/A good for about 10–14 days, and lists minimum rates for 4–5 weeks of control (at least 2 oz Valor SX, 6 oz Authority/Spartan 4F, 2 oz Zidua WG, 5–6 oz metribuzin 75 DF).
- Emergence outlasts any PRE: Iowa State reports waterhemp emerging May through August at up to 1 to 1¼ inches a day, and in Ohio no soil-applied herbicide gave season-long control, so a postemergence pass was necessary.
- Weather breaks residuals: in the Iowa 2015–19 data flumioxazin fell below 60% in one of five years and the Group 15 actives fell below 50% at their worst, with early breakdown in the wet spring of 2019.
- Resistance narrows the options: almost 25% of 75 Iowa waterhemp populations collected in 2019 carried four-way resistance, and the Purdue screening population was ALS- and glyphosate-resistant with PPO resistance below 15%.
- The yield evidence is one trial: Minnesota 2015 layered treatments yielded 46 to 51 bu/ac against 32 to 43 for PRE-only and 14 for the weedy check, under 51 waterhemp per square foot on June 8.
- The Ohio trial was a single year, was not harvested, and planted June 2 after a May 16 PRE; its 70% to 99% August ratings include a Liberty pass in every treatment.
Read the sources · 5
- Performance of Preemergence Herbicides on Waterhemp Control in Soybean ↗
Five years (2015–19) of Iowa State herbicide evaluation trials with PRE products alone at labeled rates: pyroxasulfone’s lowest control was 88% at three weeks and it exceeded 95% half the time; S-metolachlor, dimethenamid-P and acetochlor gave 82% or more half the time but fell below 50% at worst; flumioxazin exceeded 95% half the time but fell below 60% in one of five years.
- Herbicide Programs for Waterhemp Control in Soybean ↗
Comparing programs at 4 weeks after application, Verdict PRE at 5 oz/a gave 70% control, rising to 90% or more when followed by Liberty plus a Group 15 POST; two-pass programs with an effective PRE and POST showed no significant differences at 90% or better, while 2,4-D choline or glufosinate alone POST stayed below 90%. Almost 25% of 75 Iowa populations collected in 2019 had four-way resistance.
- Which Residual Herbicide Should I Use for Waterhemp Control in Soybeans? ↗
Pooling Purdue screening trials from several years (at least four observations per herbicide) on an ALS- and glyphosate-resistant population: Spartan, Valor, Outlook, Zidua and Warrant gave 90% or greater control at 28 days, Valor alone or in premixes 94% or higher, Group 15 premixes 93% or greater, 4 to 6 oz metribuzin alone and Prowl in the mid-70s, and 1 oz Sharpen under 60%.
- Got waterhemp? Layer residual herbicides to maintain control ↗
Rochester, Minnesota, 2015: by the end of September waterhemp control was 90 to 95 percent in the two-pass layered program against 62 to 81 percent for a single PRE (Group 15 products Dual II Magnum, Outlook and Warrant, each with Pursuit); layered plots yielded 46 to 51 bu/ac, PRE-only 32 to 43, the weedy check 14, a 10-bushel average difference.
- Management of Waterhemp in LibertyLink Soybeans ↗
One 2017 trial near St. Marys, Ohio, four replications: residual PREs (Valor XLT, Valor XLT + metribuzin, Fierce XLT) held 82 to 84% control on June 26 before the Liberty pass, and on August 15 control was 70% with no residual, 88% for Valor XLT, 92% for Fierce XLT and 99% for Valor XLT followed by Zidua POST.
Before you buy, ask
- What disease pressure did the trials with a yield response have, and do my fields see it?
- What application timing and rate did the cited studies use?
- Is there a scouting threshold that would tell me whether to apply this season?
Record
- Sources checked
- October 12, 2026. Every figure shown is printed on the linked page; unit conversions are noted on the chart.
- Company response
- None yet. Makers and suppliers of this product can send corrections, additional trials, or a statement; it is published here, labelled, and never edits the research summary. Send a correction →