In the year 2000 Weed scientist and Area Agriculture Agent Barry Tickes from the University of Arizona Yuma Agricultural Center conducted many evaluations to determine the best application method for Pronamide Herbicide (Kerb) in lettuce. His studies revealed that in the low desert the product was losing significant efficacy because it was applied right after planting and before starting sprinkler irrigation. Pronamide is very soluble in water and was often leached below weed seeds prior to their germination.The goal of these projects was to delay the application of the product to have it available at the right time for weed germination. To do this Tickes stopped the sprinkler irrigation at different timings before weed germination and sprayed plots with a CO2 experimental backpack in the mud. 
He demonstrated that Kerb applications should be delayed from 1 to 6 days after starting sprinklers depending on the time of the season. Delayed applications at the time were done with aerial applications, but after the terrorist’s attacks 21 years ago all air traffic was suspended. Then PCAs asked if the product could be chemigated (applied through the sprinkler irrigation). To answer this question Tickes conducted several trials in Yuma. 
Surprisingly the results revealed that the product performed better chemigated than applied by air. Today most of the Kerb in Arizona is chemigated and applied in delayed applications, also the method is extensively used in California. 
It all started with a little trial in a Yuma Experiment Station that demonstrated delayed applications work. Then 9/11created the circumstances that forced the industry to take that course. If you would like to review the original data from this research please visit: Timing Kerb Applications in Lettuce and Evaluation of Kerb Applied by Sprinkler Irrigation to Lettuce both by Barry Tickes.

Timing Kerb Applications in Lettuce