AUGUST 30, 2018 — University of Nebraska–Lincoln, CropWatch
Cody Creech – Dryland Cropping Systems Specialist

Pictured above: Figure 1. Comparison of two wheat research plots near Scottsbluff. On the left is an untreated control plot with a heavy infestation of downy brome and feral rye. On the right the same population of grassy weeds was treated with Aggressor herbicide, part of the CoAXium Wheat Production System.

A new herbicide-tolerant wheat production system was officially unveiled in 2018 and is now available to growers. The CoAXium™ Wheat Production System was developed to provide growers an additional option to control grassy annual weeds in wheat. CoAXium is the system, Aggressor™ is the new herbicide, and AXigen™ is the patented trait that confers the herbicide tolerance.

Colorado wheat growers identified a need for a Clearfield® alternative and were the ones who pushed for a new system. The Colorado Wheat Research Foundation took the idea and provided funding to Colorado State University. CSU was able to develop the trait and successfully incorporate it into many of its breeding lines. Other partners include Albaugh LLC, a leader in post-patent agro-chemicals, and Limagrain Cereal Seeds.

Clearfield wheat was developed and released in 2001 by BASF. Initially, Clearfield wheat had only single-gene tolerance to Beyond (Imazamox), a Group 2 herbicide. Eventually, two-gene Clearfield wheat was developed and provided additional levels of crop safety and allowed the use of methylated seed oil which increased the effectiveness of the herbicide. The Clearfield Production System became the best method for growers to control problematic annual grassy weeds such as downy brome, jointed goatgrass, or feral rye. However, continued reliance on this system to control these problematic weeds has led to herbicide resistance in some areas. In addition, environmental conditions around the time of application must be ideal for Beyond to be effective.

What You Need To Know

  • All CoAXium wheat varieties will have two genes of tolerance and excellent crop safety. They can be identified by the AX suffix. Varieties available in 2018 include PlainsGold Incline AX and LCS Fusion AX.
  • Growers must purchase new certified seed each year and adhere to a stewardship agreement. Saving seed to replant is not permitted.
  • Aggressor herbicide is a Group 1 ACCase-inhibiting herbicide with the active ingredient quizlafop-p-ethyl. If applying a herbicide with quizlafop-p-ethyl to CoAXium wheat, only Aggressor brand herbicides registered for use can be used. New formulations of Aggressor are being developed to provide broadleaf control and will be available in the future.
  • Aggressor herbicide only has grassy weed activity and a broadleaf herbicide must be used to control broadleaf weeds.
  • Adjuvants recommended include MSO, COC, and NIS. Aggressor can be applied with nitrogen-based foliar fertilizers.
  • Never tank-mix MCPA amine or 2,4-D amine formulations with Aggressor herbicide. This can be very antagonistic and reduce the efficacy of Aggressor on grassy weeds.
  • Beyond (Imazamox) will kill CoAXium wheat, Aggressor will kill Clearfield wheat, and both will kill non-traited wheat. Care should be taken to avoid misapplications.
  • Application rates are 8-12 fl oz per single application and 8 fl oz for a split application (fall/spring) not to exceed 16 fl oz in a season.

Should You Consider Using CoAXium Wheat in 2018?
The two commercial varieties which have been released for use in 2018 are PlainsGold Incline AX and LCS Fusion AX. Due to some production issues (hail) at some of the seed increase fields, seed quantities are very limited this year. If seed becomes available, a grower may consider seeding some in a small weedy area of a field to become familiar with the technology. It also could be seeded in a field that has grassy weeds that the Clearfield production system is no longer able to control. Neither PlainsGold Incline AX nor LCS Fusion AX performed well in performance variety trials in 2018 and should not be used on a majority of a farm’s acres. Furthermore, they are not well adapted to Nebraska. These varieties will be short lived and quickly replaced by better yielding varieties in the coming years. Limagrain, CSU, and UNL are all working on developing new varieties with the AXigen trait.

Nebraska Research Results
The Dryland Cropping Systems Program at the Panhandle Research and Extension Center has partnered with Albaugh LLC the past three years to assist in developing use recommendations for Aggressor. Aggressor herbicide was evaluated at many rates, with different nozzles, carrier rates, adjuvants, and timings. Here are some of the things we learned:

  • No crop injury was observed with Aggressor when applied between the 4-leaf and stem elongation growth stages.
    It performed well under a variety of environmental conditions.
  • Aggressor at a 10-12 fl oz rate was needed for control of feral rye and jointed goatgrass.
  • Aggressor at a rate of 8 fl oz rate was sufficient for downy brome control.
  • If grassy weed pressure is high, use a fall application followed by a spring application
  • Antagonism with tank-mix partners reduces efficacy. Only tank-mix with approved herbicides.

Stewardship Guidelines
Stewardship of this new technology is critical to maximize efficacy and longevity of this production system. Growers must sign and adhere to a stewardship agreement. As part of this agreement, growers must purchase certified seed and follow the Aggressor herbicide label. Integrated best management practices include limiting the sole use of Aggressor herbicide to control grassy weeds. Growers should rotate to other crops, use a fallow period, rotate herbicide modes of action, use proper timing of glyphosate in fallow year to limit weed seed production, or use Clearfield wheat to reduce selection of herbicide-resistant weeds caused by repeated use.

Article courtesy of CropWatch — A central resource for University of Nebraska–Lincoln Extension information on crop production and pest management. It is written by Extension Educators and Specialists and produced by IANR Media in the UNL Institute of Agriculture and Natural Resources.