Managing Weeds in Soybeans with Timely Herbicide Use

Monday, June 16, 2025

Spring fluctuating weather has created inconsistent conditions for soybean planting and spraying. While some farmers have successfully applied burndown and residual herbicides before planting, others have planted before spraying complicating postemergence (POST) weed control.

Problematic weeds like dandelion and herbicide-resistant marestail (horseweed) are especially hard to manage after soybeans emerge.

Additionally, many commonly used soil-applied herbicides such as Valor, Authority, Sharpen, and metribuzin are not suitable for over-the-top applications due to potential crop injury.

Fortunately, several herbicides are approved for POST use and offer either foliar or residual control of broadleaf weeds. However, some are limited in effectiveness against perennials like dandelion, burdock, and curly dock.

Residual herbicides such as Dual Magnum, Outlook, Warrant/Enversa, and Zidua/Anthem Maxx do not kill existing weeds and must be tank-mixed with foliar-active products for full-spectrum control.

Key POST herbicides include:

Anthem Maxx: Used PRE or POST (up to the 6th trifoliate), offers residual control via pyroxasulfone.
Basagran and Cadet: Target small annual broadleaves, especially velvetleaf and pigweeds.
Classic/Synchrony and Cobra: Effective on ragweed, smartweed, and pigweeds; Cobra is typically applied early POST.
Enlist One: For Enlist E3 soybeans only; controls a wide range of broadleaf weeds.
Glyphosate: Works well on many species, except glyphosate-resistant weeds.
Liberty 280/Ultra: For glufosinate-resistant soybeans; strong on annuals including Palmer and marestail.
FirstRate, Harmony SG, and Ultra Blazer: Effective on several broadleaves but limited against resistant marestail.
Outlook and Zidua: Provide residual control only, best tank-mixed with foliar products.
Pursuit, Raptor, Reflex/Flexstar, and Python: Offer a mix of foliar and residual control depending on timing.

Timely applications and appropriate tank mixes are essential. Refer to the 2025 Penn State Agronomy Guide, Table 2.4-14, for detailed herbicide recommendations, rates, and precautions. Always follow labeled application windows and safety intervals to avoid crop damage and ensure optimal weed control.

Photo Credit: istock-urpspoteko