Oak Worms

Oak worm (Phryganidia California) is one of the most damaging insects in California. The cyclical nature of its population causes it to be more common in some years and almost absent in other years. Damage is most common to the coast live oak (Quercus agrifolia) in the San Francisco bay area.

Eggs are white and then develop red centers that fade to pink before hatching. They are laid on limbs, leaves, and bark. Larvae are dark with yellow or olive stripes, growing to one inch in length.

Young larvae chew all the way through the leaf, leaving a skeleton like appearence. Defoliation on live oaks may become extensive in May or June and again in July through September. Healthy trees can tolerate some damage, but trees under stress from drought or other factors may decline if defoliation is extensive.

Monitoring and prevention are most important when controlling the Oak Worm. Defoliation will occur if oaks are not treated. Application of natural and synthetic controls are available for control of the Oak Worm. Applications are most effective while caterpillars are in the young stage.

Please call or email City Arborist Tree Care to discuss your tree’s disease and pest control needs.