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Oak Worm

oak worms

Photos courtesy of Larry Costello PhD - University of California


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.

Arborwell Tree Service's Wellness Approach

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.

Download a PDF about Oak Worm as part of a Tree Wellness Program

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To speak with an Arborwell Wellness Specialist, please call 888-969-8733. Our team of ISA certified arborists are ready to help with all your arboricultural needs.

Pruning & Removals are not part of the tree Wellness programs

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