Soybean Herbicide Considerations

By Dwight Lingenfelter

Due to the weird spring weather, soybean planting and spraying has been rather erratic. Some have been able to spray burndowns and residuals and plant in a timely manner while others have yet to spray but the beans have already been planted. Weeds like dandelion, resistant marestail/horseweed, etc. will be very difficult to control postemergence in soybean. Also, many of the typical soil-applied residual soybean herbicides (e.g., Valor, Authority, Sharpen, metribuzin, etc.) cannot be applied over the top of soybeans because of injury concerns. Below is a list of herbicides that have foliar broadleaf activity and/or residual activity and are allowed POST along with their labeled application timings and strengths. Unfortunately, many of these herbicides will not handle dandelion, burdock, curly dock, etc. very well. Keep in mind that products such as Dual Magnum, Outlook, Warrant, and Zidua will not control emerged weed, so they will need to be tank-mixed with herbicides that have foliar activity. Additional details about these herbicides can be found in Table 2.4-14 of the 2021-22 Penn State Agronomy Guide . This is not a comprehensive list and excludes generic products and herbicides that are mostly active on grasses (e.g., clethodim, Assure II, etc.) and/or not typically applied POST.

• Anthem Maxx – can be applied either PRE or POST up to the 6^th trifoliate but at least 60 days before harvest. Since it contains Cadet some annual broadleaves (not marestail) will be controlled during burndown but it tends to be weak on perennials. The pyroxasulfone (Zidua) portion will not control existing weeds but will provide residual activity on annual grasses and small-seeded broadleaves.
• Basagran – after emergence (general control of small annual broadleaves – good on cocklebur, lambsquarters, smartweed, and velvetleaf).
• Cadet – Preplant through full flowering (general control of small annual broadleaves – good on lambsquarters, nightshade, pigweeds, and velvetleaf).
• Classic (or Synchrony) – at least one trifoliate leaf up to 60 days before maturity (general control of small annual broadleaves – good on cocklebur, jimsonweed, pigweeds, and smartweed).
• Cobra – apply PRE or POST up to 45 days before harvest- one to two trifoliate leaves is typical (general control of small annual broadleaves – good on jimsonweed, nightshade, pigweeds, ragweeds, and smartweed).
• Dicamba products (Engenia, Xtendamax, Tavium) – for use in Xtend soybean varieties only; soybean emergence thru June 30. Controls many annual and perennial broadleaf weeds.
• Dual Magnum – can be applied POST but the exact application timing is not specified but at least 90 days before harvest. It will not control existing weeds but will provide residual activity on annual grasses and small-seeded broadleaves and nutsedge.
• Enlist One – can be applied in Enlist E3 soybean varieties only from emerge to no later than full flower stage (R2). Controls many annual and perennial broadleaf weeds. Enlist Duo contains glyphosate.
• FirstRate – 1st soybean trifoliate through 50% flowering (general control of small annual broadleaves – good on cocklebur, ragweeds, and velvetleaf; will not control ALS-resistant marestail).
• Glyphosate (Roundup Ready or glyphosate-resistant varieties only) - emergence through flowering. Overall good weed control of many species but it can be weak on perennials such as dandelion and glyphosate-resistant weeds such as marestail.
• Harmony SG – after 1st trifoliate has expanded fully and no later than 60 days before harvest (general control of small annual broadleaves – good on lambsquaters, pigweeds, smartweed, and velvetleaf).
• Liberty 280 (Liberty Link or varieties than include glufosinate-resistant traits such as Enlist E3, XtendFlex, and LLGT27) – emergence through bloom. Broadspectrum control of many small annual weeds (including marestail, Palmer amaranth, waterhemp) but tends to be weak on many perennials.
• Outlook – can be applied POST from soybean cracking to 5^th trifoliate. It will not control existing weeds but will provide residual activity on annual grasses and small seeded broadleaves.
• Perpetuo – can be sprayed from soybean emergence to 6^th trifoliate. It contains Resource, which is excellent on velvetleaf, and provides suppression of certain annual broadleaves (but not marestail, Palmer amaranth or waterhemp). The pyroxasulfone (Zidua) portion will not control existing weeds but will provide residual activity on annual grasses and small-seeded broadleaves.
• Pursuit – PRE to before bloom and 85 days before harvest (general control of small annual broadleaves and some grasses – good on cocklebur, pigweeds, smartweed, and velvetleaf).
• Python - PRE and from 1st to 5^th trifoliate (generally will not control emerged weeds, but provide residual control of annual broadleaves).
• Raptor – early POST and before bloom (general control of small annual broadleaves and some grasses – good on cocklebur, lambsquarters, pigweeds, and velvetleaf).
• Reflex or Flexstar (or Flexstar GT with glyphosate) – PRE to within 45 days of harvest (Prefix also has an early POST label) (general control of small annual broadleaves – good on jimsonweed, pigweeds, ragweeds, smartweed, and velvetleaf).
• Ultra Blazer - soybeans should have at least one to two trifoliate leaves (general control of small annual broadleaves – good on jimsonweed, pigweeds, nightshade, common ragweed, and smartweed).
• Warrant – emergence to R2; but label recommends application at V2-V3 state (will not control emerged weeds, but provides residual control of annual grasses and some broadleaves). Warrant Ultra contains fomesafen (Reflex) and is designed to be applied POST (emergence to R2 stage).
• Zidua – can be applied POST from soybean cracking to 6^th trifoliate. It will not control existing weeds but will provide residual activity on annual grasses and small-seeded broadleaves including Palmer amaranth and waterhemp.