Pest profile

Elongate Hemlock Scale

Fiorinia externa · Hemiptera: Diaspididae[2]

Elongate hemlock scale yellows evergreen needles, causes needle loss and dieback, and can kill heavily infested trees.[1]

Elongate hemlock scales, oblong brown scale covers on the underside of a conifer needle
Elongate hemlock scales, oblong brown scale covers on the underside of a conifer needle. (c) Sean Grasing, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Females are about 1/20 inch with an oblong orange-brown to brown cover; males are smaller with white covers.[1]
  • Scales sit on needle undersides, and heavy infestations can make branches look gray.[1]

Where it lives

It's an invasive species best known on hemlocks and also feeds on firs, spruces, pines, cedars and yews.[1]

US map: public records from 15 states since 1990 (GBIF).

Biology and life cycle

It overwinters as fertilized females or eggs, and crawlers hatch over a long period starting around May.[1]

Because of that long hatch, all life stages can be on a tree at once.[1]

Damage and signs

  • Needles show yellow spots or bands, then yellow entirely and drop; canopies thin and branches die back.[1]

Health risk

It feeds on trees; UK Extension mentions no risk to people.[1]

Control

Pesticides

Systemic dinotefuran works; imidacloprid won't. Crawlers can be treated with horticultural oil or contact insecticides, usually several times.[1]

Common questions

Why are my hemlock needles yellow underneath?
Elongate hemlock scale on needle undersides is a common cause.[1]
Does imidacloprid control it?
No; UK Extension says imidacloprid won't be effective against this scale.[1]

Sources

  1. University of Kentucky Entomology (ENTFACT), “Dealing with Elongate Hemlock Scale (ENTFACT-471).” entomology.mgcafe.uky.edu/ef471 (accessed 2026-10-06)
  2. iNaturalist, “Fiorinia externa taxon page (order and family).” www.inaturalist.org/taxa/447063 (accessed 2026-10-06)

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