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All About Identifying and Fighting Scale Insects

What can you tell me about scale insects?

scale insects

Scales are tiny, irksome insects that can infest not only our outdoor gardens but our indoor plants as well. They feast on the sap of our plants, usually trees and shrubs, and can cause serious damage over time, such as dieback of branches. They may even eventually kill the host plant.

Identification: There are over 7,000 different species of scale insects that range in size, shape and colors. Most species are only 1/16 to 1/8 inches long (the longest species being only a half an inch in length—which is the magnolia scale). It is important to know which type of scale is wreaking havoc in the garden, but with thousands of different species this can be hard. For identification purposes, many divide the insects into two main groups: soft scales and armored scales.
Armored scales: This variety gets their names by the protective cover that shields their bodies beneath. Armored scales usually overwinter as eggs beneath the female scale’s cover and then will begin to hatch in spring as “crawlers." Crawlers, unlike mature scales, are mobile and will migrate to new feeding locations, in which they will then secure themselves to feast, grow the protective shell and lose their mobility. Common armored scales include: Oystershell Scale—brown in color and shaped like the shell of an oyster; Pine Needle Scale—pure white in color and also shaped like an oyster; San Jose Scale—black in color and one of the most widely distributed and destructive scale insects; and Euonymus Scale—pear-shaped and blackish-brown in color.
Soft scales: Usually soft scales are larger than armored scales and lack the protective shell that armored scales have. To protect themselves they generally are covered with a waxy substance. Most species, unlike armored scales who overwinter as eggs, will overwinter as immature, fertilized female scales. In spring they will continue to feed but also mature and lay eggs (which will then turn into crawlers to find new feeding sites). Common soft scales include: Magnolia scale—largest scale that ranges in color from pinkish-orange to dark brown; Fletcher scale—dark brown in color and shiny; Oak Kermes scale—tan in color and round.

Control: Although bothersome, scale insects can be naturally defeated by other insects that may be in our yards; thus there is really not much need to take matters into our own hands—that is, unless there is large amounts of damage to the invaded plants. If the amount of devastation is creating a problem, the first step is to properly identify which species of scale you may have. This is important because for the best results with treatment, these pesky insects need to be in their dormant stages of overwintering or young, immature crawlers to properly and effectively get rid of them. Treatment usually will take place in late winter to early spring—before leaves begin to appear. Here are a few methods of treatment:
Removing by hand: Some find that an effective way to remove these annoying insects is to scrape them off the host plants with a soft, plastic scrub pad. This method, however, is not the quickest or easiest option.
Pruning: You can also prune heavily infected branches of trees and shrubs to help keep the plants healthy and lower the risks of further damage by controlling the number of scales. Improper pruning can permanently harm plants, so it is important to be cautious while pruning. (For branches thicker than 1 inch, try the 3-cut method.)
Horticultural oils: Horticultural oils, or dormant oils, will cover the scales and smother them. Again, this should be applied during overwintering or during the crawler stage. Most horticultural oils will not harm the host plants, but it is important to research the labels and ask local nurseries or garden centers which ones are more environmentally friendly than others. This also holds true with insecticides. Although effective, some oils and insecticides can cause further damage to not only the plants but also wildlife and to us as well. Research is key!

Although these tiny invasive insects can potentially cause serious damage, with the proper identification and method of control, we can ensure the health and longevity of our plants.

Image: Heavy infestation of scale on dogwood shrub. SB_Johnny
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