UC Master Gardeners

The California oakworm loves to munch on oaks

UC Master GardenerMay 8, 2013 

The California oakworm feasts on oak leaves. While they may feed heavily on the trees, healthy oaks typically survive.


Q:I notice moths flying around my oak tree. Should I be concerned? — Ann M., Atascadero

A:The small gray or tan moths that you see flitting about your oak tree are likely the oak moth. About 1/2-inch in length with pronounced wing veins, the moths are commonly seen during the fall and summer months.

Two to three dozen tiny white eggs are laid on the underside of the leaves; eggs turn pink to brown before hatching. The larva that emerges is known as the California oakworm.

The oakworm, despite its name, is actually a caterpillar. This small, yellow-green caterpillar has a notable large brown head and dark stripes that run along its sides. Caterpillars extend to about 1 inch when fully grown. As the oakworm grows, it feeds on the oak tree, silently munching through the leaves.

When populations are high, defoliation may occur and can be visually alarming. During warm, dry winters, caterpillars thrive. Drought conditions may precipitate a third generation of breeding, feeding and metamorphosis. Mass “balding” throughout neighborhoods and groves may lead to the generally erroneous thinking that something must be done to save the trees.

The good news is that action is generally not required. The healthy oak can withstand quite a bit of feeding from these tiny gnawers. On occasion, the oakworm will abandon a defoliated tree in search of other food sources. These tiny herds have been known to scale walls, cross lawns and even sneak inside homes to be found hanging from draperies. Not to worry, these hapless creatures do no harm.

When food is scarce, the oakworm may head to nearby plants. Despite heavy feasting and the subsequent wear and tear on the plant, the oakworm cannot mature on nonoak species, and therefore seldom poses a permanent threat.

Management of the oak moth begins with proper care of the tree. Pesticide use is generally discouraged even when masses of oak moths ap pear overwhelming. A healthy tree will naturally attract animal and insect hunters. Birds, spiders and predatory insects all love the sight of your tree brimming with their next meal. Your best bet is to pull up a seat and enjoy the show.


Contact the University of California Cooperative Extension Master Gardeners: at 781-5939 from 1 to 5 p.m. on Monday and Thursday; at 473-7190 from 10 a.m. to noon on Wednesday in Arroyo Grande; and at 434-4105 from 9 a.m. to noon on Wednesday in Templeton. Visit the UCCE Master Gardeners Web site at http://ucanr.org/sites/mgslo/ or  e-mail mgsanluisobispo@ucdavis.edu  

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