By Barry Tickes, UA Area Agriculture Agent

Dacthal, Prefar, and GoalTender are the primary herbicides used in the low desert on broccoli and cauliflower.

Other options include Trifluralin (Treflan), Devrinol, Stinger, Poast and Select. 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. It does not prevent weed seed germination. Dacthal 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 sometime emerge but stop growing.

To be effective, Dacthal should be concentrated near the growing points. It sticks well to the soil and needs a fair amount of water to incorporate when using sprinklers. Furrow irrigation works plus 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. The herbicide 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) adheres well to soil but works at the root tips instead of the region between the radicle and cotyledon leaves. Dacthal and Prefar are not systemic and move very little in plants. These products 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 the herbicide on most soils.

Prefar is best used on grasses, purslane, and pigweed and will control lambsquarters and goosefoot in some situations.

GoalTender (Oxyfluorfen) differs greatly from Dacthal and Prefar. It works primarily on the foliage even when used as a pre-emergence herbicide. It is used pre-emergence and postemergence and has no activity on roots or shoots.

GoalTender inhibits the production of an enzyme in the plant that leads to the destruction of cell membranes. It is fast acting, dependent on sunlight, and acts similar to a contact herbicide.

Even when used pre-emergence to the weeds, GoalTender is dependent on sunlight. The weeds must emerge from the ground. The weeds absorb the herbicide during emergence and twice the postemergence rate is normally required. Since a barrier is created on the surface, any disturbance of the soil after application can reduce control.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu