In my first full year working in my new position at Iowa State University, one challenge has stood out above all others: waterhemp control is the No. 1 priority in soybean weed management. As the harvest season closes, this is the ideal moment to plan ahead for next year and decide how to effectively tackle growing waterhemp populations in soybean fields.
Using observations from this year’s harvest, farmers should review where weeds were most concentrated, categorize fields accordingly, and assign urgency. Fields with heavy waterhemp infestation must receive top attention, while cleaner fields allow for more flexible management.
When entering the 2026 soybean season, fields with known waterhemp issues should begin with a strong preemergence herbicide program that includes at least two different herbicide groups. Incorporating both preemergence and postemergence products, especially those with residual activity, remains essential for long-term and season-long weed suppression.
Below is a detailed breakdown of recommended preemergence and postemergence herbicide options, along with insights on resistance management.
Preemergence Herbicide Options for Waterhemp Control
Key Herbicide Groups Used Before Planting
Preemergence herbicides effective against waterhemp in soybeans generally fall into four main groups: HG 3, HG 5, HG 14, and HG 15. Each group offers unique advantages for controlling small-seeded broadleaf weeds.
HG 3: Classic “Yellow Herbicides”
Herbicides such as pendimethalin (Prowl) and trifluralin (Treflan) provide solid early-season control of waterhemp and various grasses. These long-established products have proven reliable, but trifluralin requires soil incorporation, creating a logistical challenge that farmers must plan for.
HG 5: Metribuzin for Waterhemp Suppression
Metribuzin is the primary Group 5 herbicide used in soybeans. It delivers excellent control of waterhemp, including biotypes resistant to atrazine. Metribuzin is included in several soybean herbicide premixes, but farmers should be cautious of potential crop sensitivity, particularly in high-pH soils or shallow planting depths.
HG 14: Dependable PPO-Inhibitors
PPO inhibitors like sulfentrazone (Authority) and flumioxazin (Valor) have been the workhorses of both preemergence and postemergence weed programs for more than a decade. These herbicides offer strong waterhemp control, even where postemergence PPO resistance exists. They are typically most effective when paired with HG 15 herbicides for a more complete residual profile.
HG 15: Essential Residual Control Products
Traditionally labeled as grass herbicides, Group 15 products have become vital tools for long-term waterhemp suppression over the past 10–15 years. These herbicides are typically applied in combination with metribuzin or PPO-inhibitors.
Common HG 15 products include:
- S-metolachlor (Dual Magnum)
- Acetochlor (Warrant)
- Dimethenamid-P (Outlook)
- Pyroxasulfone (Zidua)
These products can be applied preemergence or tank-mixed with postemergence applications to extend the season-long residual barrier.
Postemergence Herbicide Options for Waterhemp Control
Key Postemergence Herbicide Groups
Postemergence herbicides for waterhemp control fall under HG 4, HG 10, and HG 14. Unlike preemergence products, certain postemergence herbicides can only be used on genetically modified soybean varieties with specific trait tolerances.
Older herbicide groups such as HG 2 (ALS inhibitors) and HG 9 (glyphosate) once provided excellent control but now fail against most waterhemp-resistant biotypes, limiting their usefulness.
HG 4: Dicamba and 2,4-D Herbicides
This category includes dicamba and 2,4-D, but each herbicide requires soybeans to carry the matching trait—there is no cross-tolerance.
- Dicamba products (XtendiMax, Engenia, Tavium) may be available for XtendFlex soybeans, although labeling for 2026 is still uncertain.
- 2,4-D products (Enlist One, Enlist Duo) are approved for Enlist-traited soybeans and provide reliable waterhemp control.
HG 10: Glufosinate for Broad-Spectrum Control
Glufosinate (Liberty) is a strong option for fields planted with XtendFlex, Enlist, or LibertyLink soybeans. To improve performance—especially in inconsistent weather—adding ammonium sulfate (AMS) is highly recommended.
HG 14: Effective PPO Options for Postemergence Use
PPO herbicides such as lactofen (Cobra), acifluorfen (Blazer), and fomesafen (Flexstar, Reflex) remain effective tools, though resistance is increasingly common. These herbicides can control waterhemp across all soybean varieties, regardless of trait package.