By Barry Tickes, UA Area Agriculture Agent

Not all pre-emergent herbicides kill weeds before emergence. None kill the seeds. Some are absorbed only by roots or shoots and some by roots and shoots. In all cases, the weed seed must first germinate.

Herbicides absorbed only by roots ordinarily kill weed seedlings before they emerge from the soil. These include trifluralin (Treflan), pendimethalin (Prowl) and benefin (Balan).

Herbicides absorbed only by shoots often kill weak seedlings soon after emergence from the soil. These include DCPA (Dacthal) and EPTC (Eptam). Pronamide (Kerb) is absorbed by both roots and leaves and will kill some weed species very early after emergence.

When used at pre-emergence, some herbicides including oxyfluorfen (Goal) and flumioxyzin (Chateau) are absorbed by seedling weeds only after germination and emerge through the soil where the herbicide is picked up. All of these herbicides, however, are classified as “pre-emergent herbicides.”

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