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Sandy's Garden

Euonymus Scale

White flecks on leaves are probably scale insects

By: Sandy Feather ©2009
Penn State Extension


Q. I have planting of variegated euonymus that serves as a ground cover for a steep bank in my front yard that is not doing well. When I look closely at the dying euonymus plants, the stems and remaining leaves are covered with white flecks. Are they causing my plants to die? What is it, and can I do anything about it?
  

 

A. From your description, it sounds like euonymus scale (Unaspis euonymi). This is the most serious pest of wintercreeper euonymus (Euonymus fortunei) and its cultivars, such as your variegated euonymus. Euonymus scale is easy to overlook until it has caused significant damage. Plants can die from several years of severe infestation.
  


Variegated Euonymus
Variegated Euonymus

Adult euonymus scale insects appear as small white or brown, slightly raised, immobile spots on stems and leaves. They feed with piercing mouthparts, similar to drinking through a straw. If you look at the leaves closely, you often see yellow spots where these insects are feeding. This symptom can be hard to see if the leaves are heavily covered with the insects themselves. Many people have a hard time believing that they are living creatures since they do not move or take noticeable bites out of the leaves. They damage a plant by sapping it of moisture and nutrients.
  

Euonymus scale insects are known as crawlers when they first hatch. This is when they are most vulnerable to insecticide applications.

  
Euonymus scale insects are known as crawlers when they first hatch. This is only time in their life cycle when they are mobile, and also when they are most vulnerable to insecticide applications. Crawlers wander about on the leaves and stem until they find a suitable place to settle. They insert their mouthparts into the plant and begin to feed, and as they mature, they secrete a waxy covering. The covering protects them from predators and makes adult scale insects almost impervious to insecticide applications.

Classification

Euonymus scale is classified as an armored scale, a group of insects characterized by feeding in plant tissue rather than directly in the vascular tissue.  This makes them less susceptible to systemic insecticides such as Bayer Advanced Tree & Shrub Insect Control (imidacloprid) that typically move through the plant in the vascular tissue.
  

Euonymus scale
Check the bottom side of Euonymus leaves
and stems for these white flecks

  
To control euonymus scale, start by pruning and destroying heavily infested stems. Make a dormant application of horticultural oil in early spring before new growth begins. First generation crawlers emerge from late May through June. They appear as tiny orangish-yellow specks moving around on the stems and leaves. A magnifying glass will help you to see them better, but they are visible to the naked eye. Crawlers can be controlled with applications of horticultural oil, insecticidal soap, malathion, Orthene (acephate), or Sevin (carbaryl) before they form covers and begin to reproduce. Repeat applications may be necessary due to their long emergence period, and depending on the product you choose. A second generation of crawlers emerges from late July through August that may require additional applications.
  

TREATMENT "WINDOWS"
1. Early spring  2. May-June  3. July-August

  
Avoid over-fertilizing your euonymus
in an effort to help them recover from the damage, especially with fertilizers that are high in nitrogen. Insects that feed with this type of piercing mouthpart actually benefit from excessive nitrogen. It can cause their population to skyrocket. Using compost or a mild organic fertilizer such as Garden-Tone® would be a better choice.
  


MORE

Crown Gall on Euonymus


  

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