Pest profile

Walnut Scale

Diaspidiotus juglansregiae · Hemiptera: Diaspididae[3]

Walnut scales are gray armored scales that feed on walnut, red maple, boxwood, holly and other plants, causing branch dieback.[1]

No licensed photo of this species is available yet; the identification notes below describe what to look for.

How to identify it

  • Adult females are about 1/8 inch, nearly circular, flat and gray with a reddish-brown spot; a pale yellow insect lies underneath.[1]
  • Males sometimes settle at the edge of a female's cover, and the merged covers form a daisy shape that helps confirm the species.[1]

Where it lives

UK Extension says it isn't a major pest in Kentucky, though problems have been reported on red maple.[1]

US map: public records from 5 states since 1990 (GBIF).

Biology and life cycle

There are two generations a year; crawlers emerge in mid-June and again in late August to early September.[1]

It overwinters as immature males and females that finish developing the next spring.[1]

Damage and signs

  • Feeding causes branch dieback and canopy thinning, and plants can look water-stressed; armored scales make no honeydew.[1]

Health risk

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

Control

Prevention

Keep plants healthy with sound watering and fertility, avoiding over-fertilization, which favors scale buildup.[1]

Traps and physical control

Prune out heavily infested twigs, then watch for crawlers in June and again in August or September using sticky tape.[1]

Pesticides

Horticultural oil or insecticidal soap aimed at crawlers needs thorough coverage; natural enemies usually keep this scale in check.[1]

More from NC State Extension

Walnut scales sometimes form daisy-shaped clusters when male crawlers settle under the edge of a female's round cover; there are two generations a year.[2]

Common questions

What are the gray circles with a red dot on my maple twigs?
They're likely walnut scale covers, about 1/8 inch with a reddish spot.[1]
Do walnut scales make sticky honeydew?
No; as armored scales they don't, so watch for dieback and thinning instead.[1]

Sources

  1. University of Kentucky Entomology (ENTFACT), “Walnut Scale Identification and Management (ENTFACT-436).” entomology.mgcafe.uky.edu/ef436 (accessed 2026-10-06)
  2. NC State Extension, “Walnut Scale Insect on Ornamentals.” content.ces.ncsu.edu/walnut-scale-insect-on-ornamentals (accessed 2026-10-15)
  3. iNaturalist, “Diaspidiotus juglansregiae taxon page (order and family).” www.inaturalist.org/taxa/1028807 (accessed 2026-10-06)

Updated 2026-10-15. Built from sourced records. Spot an error? Tell us.