• Snowball viburnum has clustered white flowers and fruit that resemble cranberries.snowball tree berryes image by Kokhanchikov from Fotolia.com
  
  The snowball tree (Viburnum opulus) is a native shrub to Europe, northern Africa and northern Asia and grows in the United States in USDA Hardiness Zone 3, according to the University of Connecticut. The shrub is identified by its clustered white flowers and fruit that resemble cranberries. Under normal growing conditions, the shrub exhibits hearty growth. However, scale insects can infest Viburnum opulus, which can cause serious damage and plant death if left uncontrolled.
  
  

Oystershell Scale

• Lepidosaphes ulmi, or oystershell scale, is an armored scale insect that can cause extensive localized plant damage, and, in severe cases, plant death. The oystershell scale gets its name from the protective outer layer surrounding the insect, which resembles an oyster's shell. According to Clemson University, the scale insect is a common pest of Viburnum opulus, which infests the shrub and causes branch dieback, and in severe cases, plant death. Control for the oystershell scale consists of physical removal, pruning infected branches and the use of horticultural oil in the early spring. Apply horticultural oil every 10 days so that infestation from recently hatched scale insects does not infest the shrub as well. However, Clemson University advises against using insecticides, because they can kill the natural predators of the oystershell scale.
  
  

Mealybug

• Mealybugs are a form of unarmored scale insects that suck nutrients from a variety of plant types, including the Viburnum opulus. Mealybugs infest various areas of plants including foliage, vegetative shoot apex and below the soil surface. According to the University of Florida, a byproduct of the mealybug feeding on the plant's foliage is honeydew, which attracts other damaging insects, including ants. Black sooty mold growth is also encouraged by the honeydew byproduct. Black sooty mold rarely does damage to the plant, but causes an unsightly appearance, according to Ohio State University. which recommends physically removing the insects, encouraging natural predators in the growing area and the use of a soap and water mixture at a rate of 1 tsp. per gallon.
  
  

Natural Control

• Natural control of the oystershell scale and mealybug is the best way to control plant damage. According to South Dakota State University, mealybugs and oystershell scales are susceptible to a variety of predatory insects including lady beetles, lacewings and wasps. Because the mealybug life cycle is short, refrain from using insecticides, which encourages natural predators to feed on the pests throughout the growing season. Clemson University recommends using double-faced tape on the shrub's branches to catch crawler movement of the oystershell scale. This method is effective for determining the effectiveness of biological and physical control by detecting newly hatched oystershell scale or mealybugs, known as crawlers.