WSU Extension

Hortsense

Lilac
 
Disease
Bacterial blight 
Powdery mildew 
Insect
Lilac borer 
Lilac leafminer 
Oystershell scale 



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Caption: Oystershell scales
Photo by: Unknown
  
Lilac : Oystershell scale
(revision date: 2/14/2019)


Biology
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, striped with grayish and brown bands, and elongated like an oyster or mussel shell. Infested plants may wilt or show off-color foliage. Scales can be 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.
  • Where practical, prune and destroy heavily infested branches.
  • Natural predators and parasites help control scale populations, but usually not soon enough to prevent damage to plants.
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.
  • Bonide Systemic Insect Control
    Active ingredient: acephate  |  EPA reg no: 239-2461-4
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.
Images

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Caption: Oystershell scales
Photo by: Unknown