The use of sprinklers to establish wheat following vegetables has become an increasing practice. Chemigating pesticides through sprinklers can be an effective and convenient application method. It has been used with some success with only 1 of the 15 possible wheat herbicide options in this region and is a registered use with only 2 of them.

Prowl H2O was registered for chemigation on wheat in recent years and most users have reported good control. As with any preemergence herbicide, it must be applied and incorporated prior to weed emergence. Prowl H2O can only be applied after the wheat has emerged and has one leaf and this can be too late. Additionally, where soils crack, weeds can emerge through these cracks from below the treated soil.

The other wheat herbicide used in this region that is registered for chemigation is bromoxynil(Buctril, Moxy, Bison, Maestro and other trade names). There is little use of this registration here and it can be hazardous. Bromoxynil is a contact herbicide that can cause injury to all of the broadleaf crops grown in this region. At times, sprinklers are not even a good method of applying water, let alone a contact herbicide that can move off target. It is registered for this use, however, and may be an option under some conditions. If Chemigated, it should be applied within the last 30 to 40 minutes of the sprinkler run and thoroughly washed out of the pipe.

No other wheat herbicide is registered for or would be effective applied by chemigation. The growth regulators (2,4-D, MCPA, dicamba or clopyralid) are foliar applied, systemic and volatile. Aim/Shark is a contact herbicide but is not registered for chemigation and would be hazardous to apply by this method. One of the newer wheat herbicides, thifensulfuron, was used successfully in Arizona as Unity (Gowan) a couple years ago and last season as Harmony (DuPont). This year Dupont has replaced Harmony with Affinity TankMix which is a premix of thifensulfuron and another similar herbicide, tribenuron. Harmony alone is broad spectrum and the addition of tribenuron adds little but some temporary crop injury at early growth stages. Additionally, the current label reads that users should “tank mix with other suitable herbicides”. There is an effort being made to modify this requirement. Although thifensulfuron is still a very effective herbicide, these changes will reduce its utility in this region.

The grass herbicides, Discover, Osprey and Tacoma/Puma, are not registered for chemigation. They work best when applied by ground to the growing points and would likely be ineffective when applied by sprinklers. To learn more please see the updated table for wheat herbicides.

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.