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Best of Both Worlds: Use of Glyphosate and Glufosinate (Liberty®) in conjunction with LibertyLink® GT27™ Soybeans

September 2018 

With the exciting news regarding the availability of Stine® LibertyLink® GT27™ brand soybeans for the 2019 growing season, there have been questions about how growers can maximize the technology. One question I keep hearing is, “can I spray both products on the beans at the same time?” Before answering that, growers must first understand certain characteristics regarding each of these chemistries to maximize their efficacy and prolong their usage with LibertyLink GT27 technology.

Glyphosate is a Group 9 herbicide and is considered an organophosphorus compound.  Glyphosate is a systemic, translocating herbicide that inhibits the EPSP synthase pathway. The herbicide blocks essential amino acids necessary for the photosynthetic processes of the plant. It tends to work slowly, approximately 7–14 days, and is recommended to be sprayed with coarse to large-sized droplets in 5–10 gallons of water per acre. The typical rate for 41 percent solution is one quart per acre with a water conditioning agent (ammonium sulfate) at the rate of 8–17 pounds per 100 gallons of water and the use of a non-ionic surfactant for water droplet retention on leaves. This mix results in an active ingredient composition of 13.12 ounces per acre. The concentration of lethality at this rate is dependent on the water rate that is applied to the field, so as gallons per acre increase, so must the rate of glyphosate in the tank. It is recommended to spray glyphosate when weeds are actively growing and not under stress. In addition, precaution should be taken to avoid spraying during times of intense heat and moisture stress.

Glufosinate is a Group 10 herbicide and is also considered an organophosphorus compound. However, glufosinate is a contact, semi-translocating herbicide that inhibits glutamine synthetase. It mainly kills by inhibiting a plant’s ability to utilize nitrogen and causing ammonia within the plant to become toxic to the plant. The herbicide tends to work very quickly, within 24–72 hours, and is recommended to be sprayed with medium to coarse sized droplets in 15–20 gallons of water per acre. It is recommended at rates of 29–36 ounces per acre with a carrier of ammonium sulfate at the rate of 1.5–3 pounds per acre. It is not recommended to spray Liberty with FloodJet nozzles, controlled droplet application equipment or air-assisted spray equipment. It is recommended to spray glufosinate when weeds are actively growing and not under stress. In addition, it is helpful to spray during daylight hours, in adequate temperatures (86 degrees Fahrenheit and above) with higher relative humidity.

Based on these differences, the following recommendations should be observed:

  1. It is best to utilize these products in a sequential-combined application. Use glyphosate in burndown combinations with other effective modes of action and residual herbicides. For post-emergent applications, combine glyphosate and glufosinate with additional effective modes of action and residual herbicides. This provides the best chance of overcoming nature’s ability to adapt and combat herbicide resistance. For additional effective modes of herbicide action, contact your local extension weed specialist or Stine regional agronomist.

  2. For optimum weed control and long-term effectiveness of the trait system, it is recommended to utilize three effective site-of-action herbicides per application with one of those being a soil-applied residual herbicide.
  3. Always utilize the “most restrictive” label for guidelines. In this case, that would be glufosinate (Liberty).
  4. Spray volume should be applied in the 15–20 gallons per acre window.
  5. 1.5–3 pounds of ammonium sulfate should be used per acre.
  6. Target medium to coarse droplets. A good rule of thumb is volume per acre plus pressure should equal 60. For example, if you are spraying 15 gallons, then pressure should equal 45 psi.
  7. DO NOT use the addition of non-ionic surfactants.
  8. DO NOT apply during periods of heavy dew or fog. If relative humidity is low, increase droplet size to coarse droplets to counteract evaporative loss. DO NOT apply after two hours before sunset.
  9. Anti-foam agents may help prevent excessive foaming.
  10. DO NOT apply after R1 growth stage.
  11. Rainfast = 4 hours

For more information about herbicide applications with LibertyLink GT27 brand soybeans, contact your local Stine sales agronomist.