By Amit J. Jhala, extension weed management specialist, Department of Agronomy and Horticulture, University of Nebraska-Lincoln
Early-season weed management is imperative to maximize soybean yield, and for any soybean farmers unable to apply soil residual herbicides before soybean emergence, post-emergence application of residual herbicide can be a part of the solution.
Given that most soybeans grown in the United States are glyphosate-tolerant, farmers can tank-mix glyphosate with residual herbicides labeled for soybeans to control weeds already emerged at the time of application. This adds a different mode of action and could help with glyphosate-resistant-weed management. For more information, see the University of Nebraska-Lincoln Extension’s 2014 Guide for Weed Management in Nebraska.
Options for herbicides that can be applied after emergence to provide residual control
- A pre-mix of Zidua (Pyroxasulfone) and Cadet (Fluthiacet-methyl).
- It can be applied post-emergence in soybeans up to the V3 stage.
- The application rate is between 4 fl. oz. and 9 fl. oz. per acre, depending on soil type.
- It provides effective residual activity for control of common waterhemp, Palmer amaranth, common lambsquarters, velvetleaf and grasses.
- Dual II Magnum
- Can be applied at a rate of 1 to 1.33 pints per acre.
- Use as a post-emergence treatment to soybeans from emergence up through the 3rd trifoliate leaf stage.
- It will not control emerged weeds, so it must be applied to a weed-free soil surface or in a tank mixture with products that provide post-emergence control of weeds present at the time of application.
- Do NOT apply Dual II Magnum if S-metolachlor products, such as Dual Magnum or Dual II Magnum, have already been applied.
- May be applied any time prior to the 50 percent flowering stage of soybeans. However, application prior to full emergence of the first soybean trifoliate leaf may cause temporary yellowing or chlorosis of soybeans.
- Tank-mix partners may cause other effects regardless of application timing.
- Can be applied soon after emergence in soybeans when weeds are actively growing and before they exceed a height of 3 inches.
- Apply Pursuit before soybean bloom at an application rate of 4 oz. per acre.
- Base application timing on weed size and not soybean growth stage.
- Use a crop oil concentrate at 1 gallon per 100 gallons of spray solution.
- Can be applied at 2 to 2.33 pints per acre as a post-emergence application from cracking through the 3rd trifoliate stage of soybeans.
- Necrotic spotting, leaf crinkling or curling of soybean leaves may occur following post-emergence application, but soybeans soon outgrow these effects and develop normally.
- Prefix alone may control or partially control some emerged broadleaf weeds. However, for broad-spectrum control, tank-mix with other herbicides.
- Add non-ionic surfactant at 0.25 percent of the final spray volume. Do NOT use crop oil concentrate when applying Prefix post-emergence as these spray adjuvants may increase soybean injury.
- A selective residual herbicide for controlling annual broadleaf, grass and sedge weeds.
- Emerged weeds will not be controlled and must be controlled with an appropriate post-emergence herbicide.
- Outlook can be applied from emergence to 5th trifoliate leaf stage.
- The application rates in a single application are 12 fl. oz. to 18 fl. oz. per acre on coarse-texture soils and 14 fl. oz. to 21 fl. oz. per acre on medium-texture or fine-texture soils.
- This can also be influenced by soil-organic-matter content.
- If Outlook is applied in two split applications, maintain a minimum 14-day interval between applications and do NOT exceed a seasonal total of 24 fl. oz. per acre.
- An encapsulated acetochlor herbicide that can be applied after soybeans after soybeans are completely emerged, but before they reach the R2 (initiation of flowering) growth stage.
- It can be applied at 1.25 to 2 quarts per acre, depending on soil texture and organic matter content.
- The optimum timing and rate of application are when soybeans are V2 to V3 stage at 1.5 quarts per acre.
- Warrant is a residual herbicide, so it must be tank-mixed with a burndown herbicide to control existing weeds.
- A selective, rate-dependent residual herbicide for control of annual grasses, broadleaf and sedge weeds.
- It can be applied to soybeans at first to third trifoliate leaf stage.
- Do NOT apply Zidua to soybeans from emergence (at cracking) through unifoliate stage or injury may occur.
- The early post-emergence application rate is in a range of 1 oz. to 3.5 oz. per acre, depending on soil texture.
- Zidua has no foliar activity, so it must be tank-mixed with a foliar active herbicide for control of existing weeds.
Tank-mix partners may cause other effects regardless of the application timing. Always read labels before applying herbicide in the field, and follow application timing and other restrictions of tank-mix herbicide partners as noted in the herbicide label.