Euonymous Scale

Euonymous scale, a serious pest of euonymous, pachysandra, and bittersweet, is a common arrival at the UK Insect Identification Lab. Given time, these armored scales can encrust stems and foliage of plants causing yellowed foliage, stunted growth, and branch dieback.

The distinctly different waxy coverings of females and males (Figure 1) gives the appearance plants are being attacked by two species.  The males have emerged and mated so only their empty coverings remain. Fertilized females will spend winter under the waxy cover and begin to lay eggs from late April through May for the first of two annual generations.

Figure 1. Pear-shaped brown and gray (female) and smaller, narrow white (male) euonymous scale coverings. (Photo: Lee Townsend, UK)

Figure 1. Pear-shaped brown and gray (female) and smaller, narrow white (male) euonymous scale coverings. (Photo: Lee Townsend, UK)

Figure 2. Bottom view of a female euonymous scale. (Photo: Lee Townsend, UK)

Figure 2. Bottom view of a female euonymous scale. (Photo: Lee Townsend, UK)

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Management

Management of euonymous scale requires integrating several control tactics over time. Their waxy scale coverings protect them from insecticide applications. In addition, some individuals feeding near the base of plants can escape treatment.

Here are some steps to follow in managing this insect:

  • When practical, prune and destroy heavily infested plants in mid-spring before eggs hatch and crawlers become active.
  • Dormant oil applications can reduce overwintering populations, but overlapping scales on heavily infested plants can reduce coverage.
  • Brush off or scrape away light infestations when possible.
  • Target the newly-hatched crawler stage with insecticide sprays (soaps, summer oils, pyrethrins, etc.). Egg hatch for the first generation occurs when approximately 530 degreedays (base 50F) have occurred and about 900 degreedays for the second generation. You can get the current totals for the location nearest you by visiting the Calculating Degree Days website. Be sure to select base 50. Egg hatch occurs over an extended time so more than one spray may be needed, especially for the second generation.

 

By Lee Townsend, Extension Entomologist

 

Posted in Landscape Trees & Shrubs