Scale Insects in the Landscape

Scale insects are among the most serious pests of shrubs and trees in the landscape.  Scale insects fall into two groups - armored (or hard) scales and soft scales.  Both types of scale insects secrete a cover which protects them from weather, predators and insecticides. You can identify the scale by the type of cover it has and other characteristics. Scale identification may be important in selecting the proper control.

Armored scale identification:

The scale insect’s cover is separate from the body. If you flip the cover off an armored scale, the insect beneath it will remain intact.

Armored scales feed on the contents of plant cells and do not produce honeydew.

Soft scale identification:

The scale insect’s cover is part of the skin of the insect. Flipping the cover of a soft scale tears the insect's body apart. 

Soft scales feed in the conductive elements of the plant, the xylem and phloem.  Like aphids and whiteflies, the soft scales produce lots of honeydew.  This coats the foliage below with shiny, sticky liquid and supports the growth of sooty mold. 

There can be as many as 5 or 6 generations of scales per year for some species, but most have just one or two.  Some soft scales give birth to living young, but most lay eggs that hatch into mobile crawlers.  The crawlers move out from under the cover of the female and settle down to feed on leaves or stems.  Once settled, most lose their legs and do not move again.  Others, like wax scale and cottony cushion scale, retain some degree of mobility throughout their lives. 

The cover is secreted beginning with the first molt and provides very effective protection for the insects from weather, natural enemies, and insecticides.  Scales can be small and hard to see, like obscure scale, or large and conspicuous like wax scale.  The main affect on infested plants is a gradual weakening that can lead to thinning of the plant’s canopy, die back and eventually death.

Contact insecticides are effective against young crawlers, but less so against later stages.  Systemic insecticides can be very effective against soft scales but only a few are effective against armored scales.  Horticultural oils are also effective, as are insect growth regulators.  The biggest challenge is usually identifying scales as the problem.  Your county Extension Agent can help you with selection of a control option.

Please share this information with others in the landscape & turf industry.

For more information:

See this publication and especially note the control measures in Table 2. Timing for ‘Approx. Crawler Activity’ in Table 1 may not be applicable to Georgia. Includes photos of some scales - http://extension.entm.purdue.edu/publications/E-29.pdf

 A type of armored scale

United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org

A type of soft scale

United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org