Compared to some other tree crops, California olives have relatively few registered preemergence herbicide options. However, several recent label changes have increased these options and a few new herbicides are currently being tested and may be registered in the relatively near future. 

Several new herbicides have been registered in other tree and vine and UC weed scientists have conducted several experiments with the support of the California Olive Commission, the USDA IR-4 Project, and the crop protection industry to evaluate their crop safety in olives. Although these herbicides are not currently registered in olive, early crop safety results have been mostly promising with penoxsulam (PindarGT), rimsulfuron (Matrix), mesotrione (Callisto), flazasulfuron (Mission), and saflufenacil (Treevix) – hopefully some of these will eventually be registered in this crop. 

Two demonstration trials were conducted in commercial table olive orchards in 2012-13 to evaluate registered preemergence herbicides. At the Corning site (Figure1), the overall weed control ratings were quite good into early summer following a March applications. Note: the Corning orchard was previously treated with glyphosate; thus the untreated plots should really be considered a “glyphosate-only” program. At the Porterville site, weed control was excellent up to 6 months after a November application with Princep, Goal/Prowl, Goal/Surflan, and both Chateau (10 oz or 6 + 6 oz) treatments.

Figure 1.Effects of preemergence herbicides on weed control in a young table olive orchard near Corning in 2013.

Figure 2. Effective preemergence herbicide program (foreground) compared to a postemergence-only program (background) 120 days after treatment in a 2013 table olive herbicide trial.

Figure 3. Preemergence herbicide control 125 days after treatment in olive orchard site near Porterville.