Applying herbicides through sprinklers can be an effective and convenient method of applying herbicides. Some herbicides are more effective when chemigated and is it possible to make applications when fields are wet. Sprinklers are designed to apply water and may not be the most accurate and uniform method of applying pesticides. Water is applied over several hours and days and nonuniformity is masked over long periods. In general, pesticides are applied in an hour or less and nonuniformity can be significant. Wind can be a major cause of nonuniformed applications. Timing is critical and it is difficult to change schedules to avoid windy days., Based on historical data, it is possible to predict the best times to minimize the effect of wind. Paul Brown, Extension Biometerologist at the University of Arizona has summarized how best to manage chemigation applications during windy periods:

“With the exception of days when a regional scale weather system (low pressure or frontal zone) is in or near the region, the pattern of wind flow has a distinct daily cycle wherein winds are lowest during the early morning hours, then increase from mid-morning to late afternoon, then slowly subside after sunset.

The two graphs below are from old publication that summarizes wind flow in the Yuma Valley. The dashed lines going from bottom to top on each graph represent the 25, 50, 75 And 100% percentile hourly wind speeds for each month. The solid line is the mean wind speed by hour for each month. If you track the solid lines you will see the wind speed pattern discussed above.

The bottom line for minimizing spray drift/nonuniformity is to plan to run the sprinklers during the dark hours of the day, or if not feasible, then during the first 2-3 hours after sunrise before the winds pick up.”

Cartoon: Tickes/J.Peña

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.