In June 2016, olive growers in Tulare County inquired about leaf damage that appeared to be caused by insect feeding, but no pests were directly observed.  Affected leaves tended to be in the lower canopy and exhibited scalloped edges on the leaf margin (Figure 1). The location of damage within the canopy (i.e. lower leaves), the symptomatic scalloping of affected leaves, timing of symptom onset, and lack of visible insect pests suggests that damage was caused by weevils.

Two of the most commonly encountered weevils in California olive orchards are the black vine weevil, Otiorhynchus sulcatus, and the cribate weevil, Otiorhynchus cribricollis. Both are difficult to associate with feeding on olive because the adults are nocturnal and only observed with the aid of a flashlight at night. Adult weevils consume leaf margins leaving characteristic scalloped edges. Although the damage appears alarming, mature trees typically do not withstand economic damage from the insects.  Young trees, however, may benefit from management of the insect pests. 

Damage to foliage is typically observed in late spring to early summer when adults emerge, migrate up the trunk, and begin feeding on foliage. Consequently, damage is most often observed on foliage of the lower canopy and suckers. Juvenile weevils overwinter and feed on tree roots.

View the UC IPM website for a description of the pest, as well as steps that can be taken to manage high populations of weevils in olives.  The site recommends pruning lower branches and applying bands of sticky material to tree trunks to prevent the insects from crawling from the soil into the trees.   http://ipm.ucanr.edu/PMG/r583301511.html

Acknowledgement:  We thank Dr. Marshall W. Johnson for his review prior to posting.

Scalloped leaf edges in olive trees indicate feeding by adult weevils.  Photo: Elizabeth Fichtner.