Weed control is a critical component of successful crop production, as weeds can reduce yields and lead to decreased profits for growers. Common ragweed, waterhemp, Palmer amaranth and other problem weeds can emerge at any time and if left uncontrolled, can devastate an entire soybean crop. It is important to plan ahead and take a proactive approach to weed management instead of waiting until weeds emerge.

According to the Weed Control Guide from the University of Illinois, losses in U.S. crops due to uncontrolled weeds exceed $8 billion annually, despite large expenditures for weed control. Uncontrolled weeds compete with crops for water, nutrients and sunlight, and have the potential to harbor insects and diseases, which can infest the field and affect future crops.

Emerging soybean plants are especially susceptible to pests and weeds. Soil moisture, light and nutrients are vital for soybean development, and if left untreated, weeds rob soybeans of those life-giving nutrients and lead to severely decreased yield potential.

Studies led by Bryan Young, Ph.D., at Southern Illinois University proved that significant benefits can come from using a pre-emergence herbicide followed by a post-emergence glyphosate application. However, application timing of both the pre- and post-emergence herbicides is critical to the success of the early-season weed control program. When a pre-emergence herbicide was applied before an application of glyphosate, the average yield was about 47 bu/A. However, in fields that did not receive a pre-emergence treatment, yield declined significantly. If glyphosate was applied when weeds were still 0- to 4-inches tall, average yield was 44 bu/A. If glyphosate was applied later, when weeds were 4- to 8-inches tall, average yield was down to only 41 bu/A. Additionally, all fields that did not receive the pre-emergence application also required a second glyphosate treatment, meaning another trip across the field for growers.

According to the Iowa State University Extension, in addition to increased yield, other benefits of using a pre-emergence herbicide include better time management in the spring, a wider window of opportunity to make post-emergence treatments, environmental stewardship and improved profitability. Additionally, pre-emergence residual herbicides with multiple modes of action help reduce selection pressure on weed populations and delay the development of herbicide-resistant weeds in soybeans.

Syngenta solutions


Research has shown and anecdotal reports confirm that herbicide resistance (i.e. glyphosate, ALS and PSII) is quickly spreading across the U.S. One method to combat resistance is to apply products containing herbicides with different modes of action through all soybean growth stages. In addition to protecting valuable chemistries, implementing herbicide diversity offers several benefits including:

  • Improved performance and flexibility with existing tools.
  • Decreased weed density and reduced risk for developing herbicide resistance.
  • Yield protection and improved profitability.

For timely weed control in soybeans, Syngenta offers several herbicide recommendations including:

Glyphosate-tolerant soybean herbicide options:

  • Prefix® followed by glyphosate. Prefix, a non-glyphosate, non-ALS inhibiting herbicide option controls the most difficult weeds in soybeans, like common ragweed and waterhemp, both known to be resistant to multiple herbicide modes of action. Prefix can protect potential yield with up to five weeks of residual control of highly competitive grass and broadleaf weeds, allowing a properly timed application of glyphosate as a post-emergence follow-up treatment.
  • Boundary® followed by Flexstar® GT 3.5: Boundary herbicide contains two non-ALS inhibiting, non-glyphosate and non-PPO inhibiting chemistries for managing tough weeds and grasses, including ALS- and glyphosate-resistant weeds. Follow Boundary with Flexstar GT 3.5 for two herbicides with additional modes of action, fomesafen and glyphosate, to keep fields clean through harvest.

LibertyLink® soybean herbicide options:

  • Prefix or Boundary followed by Liberty plus Dual Magnum®: Prefix and Boundary provide strong non-glyphosate, non-glufosinate pre-emergence weed control options for LibertyLink soybean systems and reduce selection pressure on this emerging technology. Follow with a post-emerge application of Liberty plus Dual Magnum herbicides to increase spectrum of control and protect the longevity of LibertyLink technology.

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