Dacthal, Prefar, and GoalTender are the primary herbicides used in the low deserts on broccoli and cauliflower. Other options include Trifluralin (Treflan), Devrinol, Stinger, Poast and Select. All of these herbicides have different characteristics and should be used differently for maximum weed control and crop safety.

Dacthal(DCPA) is effective only when applied prior to weed emergence but does not prevent weed seed germination. It is absorbed at the growing points between the radicle and cotyledon leaves. This is called the coleoptile on grasses and the hypocotyl on broadleaf weeds. Weeds sometimes emerge but stop growing. To be effective, this herbicide has to be concentrated near these growing points. It sticks strongly to the soil and needs a fair amount of water to incorporate it when using sprinklers. Furrow irrigation works as well if the bed tops are thoroughly moistened. Applying Dacthal to dry soil and incorporating it with light amounts of sprinkler or furrow water does not work. It works best when the soil is moist at application. Dacthal is fairly broad spectrum but is weak on mustards, sunflower and the thistle family.

Prefar(Bensulide) also adheres very strongly to the soil but rather than working on the region between the radicle and cotyledon leaves, it works at the root tips. Both Dacthal and Prefar are not systemic and move very little in plants. They work only where the roots and shoots contact them. Prefar must be incorporated with large amounts of sprinkler water or chemigated. Furrow irrigation, even when it thoroughly moistens the bed, will not incorporate this herbicide on most soils. Prefar is best on grasses, purslane and pigweed and will control lambsquarters and goosefoot in some situations.

GoalTender(Oxyfluorfen) differs greatly from both Dacthal and Prefar. It works primarily on the foliage, even when used as a preemergence herbicide. It is used both preemergence and postemergence and has no activity on roots or shoots. GoalTender inhibits the production of an enzyme in the plant that leads to destruction of cell membranes. It is fast acting, dependent on sunlight and acts like a contact herbicide. Even when used preemergence to the weeds, it is dependent on sunlight and the weeds must emerge from the ground. They absorb the herbicide as they emerge and twice the postemergence rate is normally required. Because a barrier is created on the surface, any disturbance of the soil after application can reduce control.

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.