Soil residual herbicide options after soybean emergence
Early-season weed control is imperative to maximize soybean yield. Many soybean growers were not able to apply pre-emergence, residual herbicides prior to soybean emergence. A few residual herbicides such as Anthem, Dual II Magnum, FirstRate, Intrro, Outlook, Prefix, Pursuit, Warrant, and Zidua can be applied after soybean emergence. Some of these herbicides such as Anthem, FirstRate (only for broadleaf weeds), Pursuit, and Prefix have foliar activity to control small, emerged weeds.
Given most soybeans grown in Nebraska are glyphosate-tolerant, glyphosate can be tank-mixed with residual herbicides with no foliar activity, such as Dual II Magnum, Warrant, or Zidua to control weeds already emerged at the time of application. It is also possible to tank-mix some other post-emergence soybean herbicides such as Cadet, Classic, Cobra, Flexstar GT, Fusilade DX, Phoenix, Ultra Blazer, and Select Max to control emerged weeds. This would add a different mode of action and might effectively delay or control glyphosate-resistant weeds. Tank-mix partners may cause other effects regardless of the application timing. Follow application timing and other restrictions of tank-mix herbicide partners as noted in the herbicide label.
Several important factors should be considered when addressing weed control with residual herbicides applied after soybean emergence:
- soybean growth stage,
- tank mix partner, and
- weed growth stage
Following is more specific information for residual herbicides that can be applied after soybean emergence.
Anthem is a pre-mix of Zidua (Pyroxasulfone) and Cadet (Fluthiacet-methyl). It can be applied post-emergence in soybean up to the V3 stage. The application rate is in a range of 4 to 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 as a post-emergence treatment to soybeans from emergence up through the 3rd trifoliate leaf stage. Dual II Magnum 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.
FirstRate may be applied any time prior to the 50% 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.
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