What are the brown bumps on my oak twigs?

Often lecanium scales, rounded brown soft scales.

Dormant oil in late fall or early spring, or soap or oil on crawlers in June and July.

Lecanium Scale: Brown Bumps on Oak, Maple and Crabapple Twigs

Females start flat and brown and become hard and rounded as they mature.^[1]
The most common in Minnesota is the European fruit lecanium scale, Parthenolecanium corni; species are hard to tell apart.^[1]

Look-alike	How to tell them apart
Other scale insects	Scale species differ in timing, so identify the species to know when crawlers are active.^[1]

Hosts include oak, maple, crabapple and many other trees and shrubs.^[1]

US map: public records from 27 states since 1990 (GBIF).

Second-stage nymphs overwinter on twigs; females lay eggs in May and June.^[1]

Crawlers hatch in June and July, feed on leaves, then return to twigs in late summer; one generation a year.^[1]

Heavy infestations can cause dieback of twigs, branches and even whole plants.^[1]

Scales feed only on plants; Minnesota Extension mentions no risk to people.^[1]

Lady beetles and parasitic wasps usually keep scale numbers low.^[1]

Horticultural oil in late fall and early spring smothers overwintering nymphs.^[1]

Insecticidal soap or oil timed to crawlers in June and July has little effect on natural enemies.^[1]

What are the brown bumps on my oak twigs?: Often lecanium scales, rounded brown soft scales.^[1]
When should I treat?: Dormant oil in late fall or early spring, or soap or oil on crawlers in June and July.^[1]

University of Minnesota Extension, “Scale insects (Yard and garden insects).” extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/scale-insects (accessed 2026-10-06)
iNaturalist, “Parthenolecanium taxon page (order and family).” www.inaturalist.org/taxa/377585 (accessed 2026-10-06)

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