Flexstar GT: A new herbicide labeled for postemergence use Roundup Ready soybean

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Flexstar GT is a new herbicide premixture recently registered by Syngenta. This premixture contains the active ingredients fomesafen (Flexstar) and glyphosate. Because of the unique modes of action of each of these active ingredients, Flexstar GT is being marketed to control weeds that are resistant to or may be harder to control with glyphosate alone. Specific weeds where this premixture may help with control are pigweeds, eastern black nightshade, and common and giant ragweed. Additionally, using the two different herbicide modes of action found in Flexstar GT may also reduce the risk of the development of herbicide-resistant weeds. Flexstar GT can be used for preplant or preemergence burndown weed control prior to soybean emergence or can be used for postemergence in-crop weed control in Roundup Ready (glyphosate-resistant) soybean only.

In Michigan, the maximum use rate for Flexstar GT is 3 pints/acre which is equivalent to 1 pint/acre of Flexstar and 1 lb ae/acre of glyphosate (42 fl oz/acre of generic formulations [3 lb ae/gal]). Similar to the restrictions for all products containing fomesafen: Flexstar, Reflex, Prefix and now Flexstar GT can only be used in alternate years. This means if you use Reflex in dry beans in one year, you cannot use Flexstar, Prefix, Reflex, or Flexstar GT the following year in soybean.

To receive the full benefit of the Flexstar (fomesafen) component in Flexstar GT, applications should be made when weeds are four inches tall or less. These early postemergence applications will also provide some residual activity from the Flexstar component. Additionally, because the Flexstar component in Flexstar GT is a contact herbicide spray volumes should be in the range of 15 to 20 gallons per acre. Flexstar GT includes an adjuvant system, however the addition of ammonium sulfate at 17 lb/100 gallons is recommended. Additionally, for in-crop postemergence applications to Roundup Ready soybeans a non-ionic surfactant at 0.25 percent v/v is also recommended. For burndown applications prior to soybean emergence, a crop oil concentrate at 1 percent v/v can be used, crop oil concentrates or methylated seed oils should not be used for postemergence in-crop applications to Roundup Ready soybean.

Additional precautions and restrictions for Flexstar GT include the following: Flexstar GT should not be applied within 45 days of harvest. Soybean, dry bean, and snap bean can be planted anytime, but small grains should not be planted for four months and corn should not be planted for 10 months. Alfalfa and sugarbeet should not be planted for 18 months. Do not apply Flexstar GT to conventional soybean.

Dr. Sprague's work is funded in part by MSU's AgBioResearch.

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