Arborjet Revolutionary Plant Health Solutions

Oak Worms

Oak Worms

There are several caterpillars that feed on oaks including the California oak worm (Phryganidia californica) and tussock moth (Orgyia spp.). Each of these caterpillars feed on oak leaves, primarily in the spring, but can be active as second generation insects in late summer or early fall. Leaves will appear skeletonized in early stages and then completely consumed as larvae mature. Feeding is usually not noticed until frass or fecal pellets fall onto underlying patio furniture or cars where they are considered a nuisance.

Oak worms are smooth, small, yellow-green caterpillars with brown heads and dark stripes down their sides. They can range from 1/10 to 1 inch in length throughout their development. Tussock moth larvae are very distinctly hairy with three prominent creamcolored dots towards the head capsule.

In California, oak worm is most commonly found on coastal live oak in San Francisco, Monterey Bay, Santa Barbara, and other areas close to water sources. Tussock moth is common in San Francisco but can also be found along the Central Coast.

Print PDF

A: California oak worm
B: Tussock moth (larvae)
Photo A taken by: Dawn Fluharty, Arborjet
Photo B taken by: Herbert A. ‘Joe’ Pase III, None,


Healthy oaks affected by oak worm experience defoliation in the spring and throughout the summer from one or more of these pests. Damage may appear sporadically or thoughout the entire canopy. Many leaves appear partially chewed (skeletonized) and will turn brown and die, while other leaves may be completely eaten. Oaks that are experiencing other stresses, such as drought, can decline from oak worm infestation at a quicker rate. Look for signs of leaf feeding or fecal pellets around the base of the tree for activity or worms raining down on you.


Trees that are in known areas of infestation can be treated preventatively in the early spring with TREE-äge® using rates according to the diameter size on the label at least 4-6 weeks prior to activity. Trees with current canopy infestations should be treated with ACE-jet for rapid response and then sequentially with TREE-äge for two years of control.

Early spring applications provide the most protection from feeding damage but later treatment will also stop mid- or latesummer infestations very well. Be sure to encourage watering of trees in naturalized areas that may have low soil moisture or natural rainfall in order to help upward distribution of the material into the canopy. Use of a soil surfactant such as NutriRoot™ in combination with watering will ensure deeper water penetration into the root system and ultimately better translocation of the systemic insecticide.

When to Treat

What to Expect After Treatment

Related Videos

Video Library

Uploaded: 10/12/2015

More videos about Oak Worms »

Treat Now, It's Easy!

Hire a Professional

Find a Distributor

Don't wait until spring!

Current Pest Warnings

Emerald Ash Borer

Threatening over 20 states in the U.S. Learn More

Pine Bark Beetles

Threatening pines in Southern and Western U.S. Learn More

Rugose Spiraling Whitefly

Nuisance pest affecting trees in S. Florida Learn More