Timing the application of preemergent herbicides for summer weed control is not an exact science. Most of the preemergent herbicides used here last at least 3 month and you just need to be sure that they are applied before the weeds germinate. The time when they germinate will vary from year to year, field to field and even within a field. The best that you can do is to assume they will germinate around February 1 and apply the herbicide then or as soon as the field is ready around that date. This corresponds to Ground Hog Day so just remember to make applications around this event regardless of what Punxsutawney Phil says. Most of the preemergence herbicides last about 3 months depending on soil conditions in the field so you are likely going to need a second application before then. Some herbicides like Eptam are extremely volatile and may last only 2 to 3 weeks and will need to be reapplied more frequently.

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.