WSU Extension


Armillaria root rot 
Collar rot 
Leaf scorch and leaf roll 
Powdery mildew 
Brown soft scale 
Lecanium scale 
Oystershell scale 

print version| pdf version| email url    
Caption: Oystershell scales
Photo by: Unknown
Dogwood : Oystershell scale
(revision date: 3/22/2021)

Oystershell scale insects are usually found on trunks, branches, and twigs. They occur less frequently on the leaves and other plant parts. The mature scale is approximately 1/8" long, brownish or gray in color, and usually elongated like an oyster or mussel shell. Infested plants may show off-color foliage. Scales are spread from plant to plant by birds, people, wind, or insects.
Management Options

Non-Chemical Management
  • In minor infestations it may be possible to wipe scales off branches.
  • Prune and destroy heavily infested branches.
Select non-chemical management options as your first choice!

Chemical Management

Scout for crawlers. Insecticide applications can be effective when applied to control the immature crawlers stage, usually in late spring to early summer. Oils are effective in the delayed dormant period. Use superior type oil sprays only on overwintering nymphs. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium salts of fatty acid  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.

+ Show larger images

Caption: Oystershell scales
Photo by: Unknown