University of Maryland Extension

Soft Scales - Trees and Shrubs

close up cottony camellia scale
Cottony camellia scale

Also see Armored (hard scales) for additional scale insects.

Scale insects belong to a large group of sucking insects that attack a wide variety of trees and shrubs. Generally, they are divided into two categories, armored (hard) and soft scale.  Heavy infestations may cause leaf yellowing, stunting, and dieback.
Eggs are laid under female adult coverings. Typically, eggs hatch in spring or summer. The stage after the eggs hatch is the immature stage or commonly called the 'crawler' stage because they walk about on plants to find new feeding sites. This is how a scale infestation spreads. 

Soft scales:

  • Appear as raised bumps on twigs and branches and can be scraped off.
  • They may be over 1/3 inch when mature and can vary in color. 
  • Produce honeydew (a sweet liquid, secreted by aphids and some (soft not armored) scale insects as they feed on plant sap) and sooty mold (a fungus that grows on honeydew), which may be present on leaves below infested branches. 
  • Honeydew can drip on to to cars parked under trees or patios and is often the first noticable sign of a scale infestation. 
  • Common examples include azalea bark scale, Magnolia scale, Indian wax, cottony camellia scale, and European fruit lecanium.  

Soft Scales Found on Trees and Shrubs - The following are examples of commonly found scale insects that infest deciduous, broadleaf, and evergreen plants. 

1) Azalea bark scale, Eriococcus azalea

azalea bark scale on stems

A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Heavy infestations over several seasons may kill plants. Overwintering immature scales (nymphs) are about 2 mm long, gray, and are usually found in twig forks. This scale primarily attacks azalea and rhododendron but has also been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. There are 2 generations a year in Maryland.

Management

2) Cottony camellia scale is also known as Cottony taxus scale 

cottony camellia scale
Close up of cottony camellia
scale
yew infested with cottony taxus scale
Cottony taxus scale on yew

3) Cottony maple scale, Neopulvinaria innumerabilis 

close up of cottony maple scale

white cottony egg masses

A native soft scale that feeds on different species of shade trees, including maple, hawthorn, dogwood, sycamore, and linden. 

Management

4) European fruit lecanium scale, Parthenolecanium corni

close up of fruit lecanium scale
Fruit lecanium scale

fruit lecanium scale on twig

Cluster of European lecanium scale
Fruit lecanium scale on twig
Photo:Bugwood.org

Contrary to its name this is a native scale. It has a varied host range but prefers maples, oaks, and ornamental fruit trees. 

Management

5) Elm scale, Gossyparia spuria

elm scale on bark

Preferred host is American elm but will infest Zelkova.

Management

6) Indian wax scale, Ceroplastes ceriferus 

close up Indian wax scale

Indian wax scale on shrub
Has a large host range which includes Chinese
and Japanese hollies, euonymus, spirea, and boxwood.
A difficult scale to control. Pruning out infested stems
and branches and gently scraping the scale
covers off bark are recommended. 


Management

7) Calico scale, Eulecanium cerasorum

close up calico scale

A native soft scale with a wide range of host plants. They include dogwood, magnolia, maple, oak, redbud, and many others. 

Management

 8) Magnolia scale, Neolecanium cornuparvum

magnolia scale on bark

This native scale is one of the largest in size. It feeds only on magnolias. 

Management

9) Fletcher scale, Parthenolecanium fletcheri 

fletcher scale

A native soft scale that can be found on evergreens like arborvitae, yew, and possibly on juniper and cypress. 

Management

10) Pine tortoise scale, Toumeyella parvicornis

pine tortoise scale

Pine tortoise scale differs from other scale insects that occur on pine. Mature female covers are 1/4 inch long, hemispherical and dark brown to black with light brown to cream colored mottling. Males are small and inconspicuous. This soft scale attacks Scotch, jack, Virginia, Austrian, Swiss mountain, red, white loblolly, shortleaf, slash and Chinese pines. It has one generation and overwinters as immatures on twigs. The damage symptoms first appear as honeydew, followed by sooty mold build up on branches. Needles turn yellow and branches eventually die. Small pines on exposed sites may are most susceptible and may be killed. To monitor for this pest, look for ants (seeking honeydew), honeydew, and sooty mold near branch terminals. In the spring the large females are found at the base of needles on twigs. Crawlers usually hatch the last two weeks of June.

Management

11) Spruce bud scale, Physokermes piceae

 spruce bud scale

Main host is Norway spruce but will infest other types of spruce. Similar looking to the buds of spruce trees so they often go undetected. They are often clustered in groups at the base of new growth. 

Management

Damage and sooty mold
photos

scale dieback on shrub
Dieback on shrub from
scale insects

thinning shrub from scale
Shrub thinning due
to scale damage

yew needles with sooty mold
Sooty mold on yew

sooty mold on sweet box foliage
Sooty mold on sweet box 
leaves below infested branch

 

Management

Scale insects are difficult to control. To manage a scale infestation, prune out branches with severe symptoms. Parasites generally provide control of many scale infestations. To protect parasites, avoid spraying with insecticides during the summer. If treatment is necessary, spray the tree with a dormant rate of horticultural oil during the dormant season to control overwintering scales. Also keep trees and shrubs watered during droughty periods and do not overfertilize. 

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