Almstead Tree & Shrub Care Blog

Thursday, September 6, 2012

Unwanted Pest #4: Scale

Our reverse countdown continues. #4 in our list of the most Unwanted Landscape Pests is Scale.

Scales are tiny insects, less than ¼”, that do almost nothing – except suck the life out of plants. There are 7,000 different types of scale insects, broadly divided into armored and soft.

Scales live boring lives. A female insect attaches herself to a leaf or shoot and begins to feed. She lays eggs beneath herself (some scale insects mate while others can reproduce without outside help) and provides shelter while they develop. “Crawlers” emerge and start to seek out their own locations. After a few days their mobility is over: they hook onto a plant and begin sucking -- forever.

Woolly Pine Scale
Source:  Terry S. Price, Georgia Forestry
  Although immobile, scales have protection. Armored scales create a hard protective covering, basically a shell. In fact, some scales are referred to as oyster shell, while others look like small pearls. Soft scales are covered in a waxy coating; they often appear as fuzzy white dots of fluff on a plant. Most release fluids as they suck; this sticky “honeydew” can cause even more problems by attracting other insects or mold – and dripping on anything below.

Scales are so tiny that they are rarely noticed until the population has increased to troublesome size. But, en masse, they can harm or even kill plants – even trees. Their lack of mobility causes them to feed in ever-increasing numbers on their host plant.

Scale’s armored or waxy coating makes them difficult to kill. They are only vulnerable to insecticide sprays during their brief crawling stage. Thorough drenching in horticultural oil or insecticidal soap can also combat scale. Finally, systemic treatments are available that cause the tree to repel the feeding insects.

Magnolia Scale
Source:  Brian Kunkel, University of Delaware,

There is no single treatment for scale insects – nor do all scale insects need to be removed. Almstead arborists and technicians examine every tree to determine the most appropriate treatment, based on factors including the type of scale, the stage of development, and the size of the tree.