How To Identify ‘Armor’ and ‘Oyster Shell’ Scale

scale 300x224 How To Identify ‘Armor’ and ‘Oyster Shell’ ScaleOne particularly common garden pest wreaking havoc on shrubs in the months of May through August is ‘Armor Scale’, also called ‘Oyster Shell Scale,’ or ‘Wax Scale.’

Identification:

Oyster Shell Scale is a peculiar looking insect, who becomes obvious on your shrubs only after it has begun to create a protective covering over itself. The shell that an active Scale creates can resemble anything from a wad of chewed gum, to a fuzzy ball on the stems and leaves of woody plants.  The white waxy ‘shell’ covering is pliable in early summer months, and emits Honeydew that the insect excretes as it feeds on the sap of a plant. Aged Scale, and dead Scale that have completed their life cycle are dry, hard, and a grey or brown color. They begin to resemble bark before they fall off a plant, but can be pruned out for appearance sake.

Scale are sucking insects, and they and their offspring (called ‘crawlers’) attach themselves to a plant within a few hours of hatching, remaining stationary for the remainder of their life while receiving the nutrients they need from sap.   Female Scale lay eggs inside of their shell, and the ‘crawlers’ emerge in late April or May to wander the plant for a one or two week window in search of a good permanent place for themselves.

While scale in small numbers are not harmful, in large numbers they can kill a plant in several ways.  Large clusters of scale will rob a plant of it’s nutrients, and stop leaf production, killing sections of a plant. Additionally, the sugary Honeydew residue can become a breeding ground for black powdery mold and bacteria, which are deadly to a plant when left unpruned. Heavy Bee and Ant activity around infested plants can be the first indicator of a Scale problem, as the two species are attracted to the Honeydew as an alternate food source.  

Oyster Shell Scale’s favorite plants include Magnolia trees, and Azalea bushes, and group planting of these trees and shrubs in gardens or hedges are considered very attractive to these pests, so outbreaks on these plants should be monitored carefully to ensure that the population is controlled in time to save the plant, or grouping of shrubs.

Treatment:

When checking your plant  for scale in the summer, look for the adult for to be contained under white waxy shells, and the young to be visible and unprotected in the month of May. Crawlers are grey and tear drop shaped, and sensitive to insecticidal soap and pesticide in this stage of development. In late summer Scale will be building their covering as they feast on a plant, and are vulnerable to horticultural oils, which smother the insect by coating the plant and the wax covered shell.  Adult Scale encased in their shell are protected from pesticide, which can’t permeate the coated armor in order to reliably kill them, so treatments of pesticides should not be relied upon to control late season pests.

For a spring through summer plan to control outbreaks, apply insecticidal soap in early April, and apply a horticultural oil monthly in May and June to ensure that you will kill the juvenile and adult forms of scale. Pesticides can be used in April to control the newly hatched Crawlers, but may inadvertently kill Ladybugs, Wasps, and other predatory insects that feed on the Scale and will help to control the population.  I advise using insecticidal soap particularly against this insect, due to the necessity of repeated application, and the mixing of insect killer and horticultural oils. Carefully read the instructions on oils and sprays to ensure a proper dosage that will not damage your plant, and avoid application in the  hot weather, or the middle of the day, when these products can damage leaf tissue.

Photo Courtesy of: Eran Finkle

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Comments

  1. Dan Vosters says:

    Am calling on behalf of the village of Combined Locks. Have a problem with what I believe to be Oyster Shell Scale..Its the last week May. We have a SMALL street of a dozen ash trees effected..
    Started out with two near a stop sign, assumed the dyback was from
    winter salts. Now those two tree’s have no leaves and the others plus private yard trees, have lost half or more of their canopy!
    Help? Do we treat to stop the spread or remove all? Am I getting to excited about this? Remember EAB is moving in the state
    of Wisconsin. Any advice appreciated thank you….Dan

  2. Amy says:

    Dan,

    I think in your case calling a Certified Arborist is the best course of action. They will be able to identify the cause of the problem and potentially save the remainder of your trees. Arborists have better equipment to treat infestations on mature trees that the hardware store tools and sprays just can’t match. If I was in your position I would call an Arborist as soon as possible, and if it seems like what they prescribe to do is feasible for you to complete yourself, you can do so later.

    Best of luck!

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  1. [...] How to Identify Armor and Oyster Shell Scale Bugs – Amy of Green Gardenista is back posting what she does best: informative posts that will help you be a better “green” (in both meanings of the word) gardener. In this post she helps you identify some common bugs and how to treat them. [...]

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