By Vipan Kumar
CoAXium™ wheat is a new herbicide-resistant (non GMO) wheat technology that contains the AXigen™ trait that was developed at Colorado State University and has resistance to the ACCase (Group 1) class of herbicides. The ACCase herbicides have good foliar activity on grasses, so the CoAXium wheat varieties provide an opportunity to use a new class of herbicides for postemergence winter annual grass control in wheat.
CoAXium wheat varieties are designated with an AX suffix. PlainsGold Incline AX and LCS Fusion AX are two CoAXium winter wheat varieties that were available for planting on a limited basis this fall. Both varieties are best adapted to western Kansas.
Aggressor is the herbicide labeled for use on CoAXium wheat. Aggressor is marketed by the Albaugh, LLC and contains the active ingredient quizalofop-p-ethyl. Do not apply Aggressor to non-AX wheat varieties (including Clearfield wheat) or wheat will be severely injured or killed. Aggressor can be applied at a single application rate of 8 to 12 fluid ounces per acre in the fall or spring, or as a split application of 8 fl. oz. in each application. Split applications should be separated by at least 14 days and most likely would be a fall/spring split. Aggressor should be applied in combination with methylated seed oil, crop oil concentrate, or nonionic surfactant to optimize performance. Applications can be made with liquid fertilizer as part of the spray carrier, but the fertilizer concentration shouldn’t exceed 50% of the total spray volume. Aggressor can be applied to wheat from the 4-leaf to the jointing stage of wheat growth for control of actively growing grasses before they exceed the 5 leaf stage. Aggressor should not be applied if the daily maximum air temperature is not expected to exceed 40 degrees F within 1 week following application. It is important to note that spring applications of Aggressor should be made when winter annual grasses have completely come out of winter dormancy or efficacy of Aggressor herbicide will be compromised.
Aggressor should provide good control of most winter annual grasses (including ALS-resistant weed biotypes) such as downy brome, jointed goatgrass, feral rye, Italian ryegrass, and volunteer cereals. Downy brome control with Aggressor herbicide treatments in CoAXium wheat at Hays in 2017-18 is presented in the Table below.
Table 1. Effectiveness of fall/spring-applied Aggressor on downy brome control in Incline AX CoAxium winter wheat at KSU Ag Research Center-Hays, Kansas in 2018abc.
Herbicide | Rate | Timing | Downy brome 4/11/18 5/6/18 | Wheat yield |
| | (oz/a) | | -----(% control)----- | (bu/a) |
Aggressor | 8 | FP | 94 | 96 | 27 |
Aggressor | 10 | FP | 94 | 96 | 28 |
Aggressor | 8 | SP | 73 | 91 | 23 |
Aggressor | 10 | SP | 69 | 91 | 23 |
Aggressor | 12 | SP | 73 | 94 | 25 |
Aggressor | 8/8 | FP/SP | 94 | 98 | 28 |
Untreated | - | - | - | - | 18 |
LSD (5%) | | | 5 | 5 | 3 |
a Fall Post (FP) was applied on Nov 6, 2017, Spring Post (SP) was applied on Mar 28, 2018. b Experimental field was under continuous winter wheat for several years. cNIS was used in all herbicide applications per label guidelines. |
Aggressor provides no broadleaf weed control and very minimal residual control. Aggressor can be tank-mixed with certain broadleaf herbicides, but should not be tank-mixed with the amine formulations of 2,4-D or MCPA or grass weed control will be severely reduced.
Figure 1. Visual response of CoAXium wheat plots treated with Aggressor herbicide in fall (A), spring (B), fall followed by spring (C) and non-treated weedy check (D). Photos by Vipan Kumar, K-State Research and Extension.
Growers will be required to sign a CoAXium stewardship agreement when they purchase certified AX wheat varieties. The stewardship agreement prohibits saving seed and limits planting CoAXium wheat varieties in the same field to every other year. Growers also agree to follow the Aggressor herbicide label guidelines to optimize performance and minimize the potential for developing ACCase resistant weeds.