By Blake Jackson
If your soybean crop is still within the appropriate growth stages, several herbicide options remain available to manage weeds effectively.
Glyphosate (Group 9) in Roundup Ready systems continues to be a useful tool against many weeds but is ineffective on glyphosate-resistant species such as marestail, Palmer amaranth, and waterhemp.
In typical Roundup Ready crops, applying glyphosate at twice the normal rate (1.5 lb ae) or making multiple in-crop applications can suppress marestail regrowth if treated soon after burndown.
However, this only slows growth rather than fully controlling these weeds. Marestail is shade-intolerant, so as soybeans canopy, they often outcompete it naturally. For Palmer amaranth, other herbicide options should be considered.
ALS-inhibiting herbicides (Group 2) like Pursuit, Raptor, Classic, Harmony, and FirstRate remain effective on many broadleaf weeds. However, ALS-resistant marestail and pigweeds are common in the region.
FirstRate and Classic, especially when combined with glyphosate, can suppress resistant marestail and work well in STS or Plenish soybean systems. Classic controls weeds like cocklebur, smartweed, and burcucumber, while Harmony targets lambsquarters and velvetleaf.
Pursuit and Raptor also manage several broadleaf weeds and grasses and can be applied to both conventional and genetically modified soybeans.
PPO herbicides (Group 14) such as Reflex, Flexstar, Cobra, Ultra Blazer, and Cadet provide control of various broadleaf species. Reflex, Flexstar, and Cobra are particularly effective against pigweeds, including Palmer amaranth and waterhemp, though they are less effective on marestail and lambsquarters.
Cadet works well on velvetleaf but is weaker on other species. These PPOs can be used in conventional, Plenish, or GM soybeans.
Glufosinate (Group 10), found in Liberty and similar products, is suitable for LibertyLink, Enlist E3, and XtendFlex soybeans and controls several troublesome weeds like marestail and Palmer amaranth.
Acetamide herbicides (Group 15), such as Dual, Zidua, Outlook, and Warrant, do not control existing weeds but provide important residual activity to suppress weeds like Palmer amaranth throughout the season.
Enlist E3 varieties allow use of 2,4-D choline products (Group 4) like Enlist One and Duo, which manage broadleaf weeds effectively but are not safe for Xtend soybeans.
It is important to note herbicide application timing restrictions as crops grow. Some herbicides can be applied late in the season, while others must be applied before flowering.
Harvest restrictions also vary, especially for silage or forage. Consult the 2025 Penn State Agronomy Guide tables for detailed ratings, application windows, and harvest intervals to ensure safe and effective herbicide use.
Photo Credit: gettyimages-gilaxia
Categories: Pennsylvania, Crops, Soybeans