Pennsylvania Soybeans: Post Herbicide Options, Application Restrictions

Emerged no-till soybeans. Photo: Dwight Lingenfelter, Pennsylvania State

Emerged no-till soybeans. Photo: Dwight Lingenfelter, Pennsylvania State

We have received some calls inquiring about post herbicide options for soybeans. If the field did not receive a burndown herbicide or a residual applied near planting, 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 primarily foliar broadleaf activity and/or residual activity and are allowed post along with their labeled application timings and strengths. Unfortunately, most 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, but they can provide residual activity of certain annual weeds, so they will need to be tank-mixed with herbicides that have foliar activity. Additional details about these herbicides can be found in Table 4-14 of the Mid-Atlantic Field Crop Weed Management Guide.

Below are brief descriptions of selected herbicides that can be applied post in soybean; keep in mind this is not a comprehensive list.

  • Anthem Maxx – can be applied post up to 3rd trifoliate but at least 60 days before harvest. Since it contains Cadet some annual broadleaves (not marestail) will be controlled by foliar contact 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, lambsquaters, smartweed, and velvetleaf).
  • Cadet – Preplant through full flowering (general control of small annual broadleaves – good on lambsquaters, 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 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/FeXapan) – for use in Xtend soybean varieties only; Applications can be made from soybean emergence up to R1 (flowering) or 45 days after planting (whichever comes first). 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.
  • FirstRate – 1st soybean trifoliate through R2 (full flower) and 70 days before harvest (general control of small annual broadleaves – good on cocklebur, ragweeds, and velvetleaf).
  • Glyphosate (Roundup Ready only) – emergence through full 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 (Liberty Link only) – emergence to bloom stage. Broadspectrum control of many small annual weeds (including marestail) but tends to be weak on many perennials.
  • Outlook – can be applied post from soybean cracking to 5th trifoliate. It will not control existing weeds but will provide residual activity on annual grasses and small seeded broadleaves.
  • Pursuit (or Extreme with Glyphosate) – 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 5th 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, lambsquaters, 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 including Palmer and waterhemp, ragweeds, smartweed, and velvetleaf).
  • Ultra Blazer – soybeans should have at least one to two trifoliate leaves and 50 days before harvest (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 provide 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 SC – can be applied post from soybean cracking to 3rd trifoliate. It will not control existing weeds but will provide residual activity on annual grasses and small seeded broadleaves.
  • Post grass herbicides – Assure II, Fusilade DX, Fusion, Poast, Select/clethodim control many annual and perennial weedy grasses and volunteer corn in soybean. See label for specific application details.

Source URL: https://extension.psu.edu/post-soybean-herbicide-options-and-application-restrictions