Pest profile

Oak Pit Scales

Asterodiaspis species · Hemiptera: Asterolecaniidae[2]

Pit scales suck juices from oak twigs, causing dieback that shows from mid- to late summer, especially on valley oak.[1]

Oak pit scale, a round greenish-yellow scale sitting in a pit on an oak twig
Oak pit scale, a round greenish-yellow scale sitting in a pit on an oak twig. (c) Stephen Thorpe, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are brown or dull green, flat, round and about the size of a pinhead, each in a pit ringed by a doughnut-shaped swelling.[1]
  • Heavy infestations make young twigs look rough and dimpled.[1]

Where it lives

Several species attack deciduous and evergreen oaks in California, with serious damage on the Central Coast and in the Central Valley.[1]

US map: state covered by the cited source.

Biology and life cycle

All adults are female and produce living young from April through October in Northern California, peaking in May and June.[1]

Crawlers move for a few days, then settle on a twig for life.[1]

Damage and signs

  • Dead leaves and twigs can hang on all winter, and severe infestations can delay leaf-out by up to three weeks.[1]
  • Heavy attacks year after year can kill young trees.[1]

Health risk

It feeds on plants; UC IPM mentions no risk to people.[1]

Control

Traps and physical control

Prune out isolated infestations if they're caught very early.[1]

Pesticides

Narrow-range oil applied in spring just before buds open, with thorough coverage, can manage small to medium trees over several years.[1]

Common questions

Why do my valley oak's twig tips die in late summer?
Oak pit scales feeding on twigs cause dieback that shows from mid- to late summer.[1]
When should I treat oak pit scale?
Oil works in spring just before buds open; once leaves are out, coverage is too hard.[1]

Sources

  1. University of California Statewide IPM Program, “Oak Pit Scales (Pest Notes).” ipm.ucanr.edu/home-and-landscape/oak-pit-scales/ (accessed 2026-10-06)
  2. iNaturalist, “Asterodiaspis taxon page (order and family).” www.inaturalist.org/taxa/375004 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.