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ARMORED SCALE IDENTIFICATION & MANAGEMENT ON ORNAMENTAL PLANTS

Steven D. Frank, Extension Entomologist

CAUTION: This information was developed for North Carolina and may not apply to other areas.
Diaspididae, HOMOPTERA

Scale insects feed on leaves or branches of many ornamental plants grown in landscapes and nurseries. They attach themselves to a plant and feed by sucking fluids through straw-like mouthparts. Scale insects can be divided into two broad categories: armored scale and soft scale. The distinction is important because behavior and management of the two groups are different. Both groups live beneath waxy covers that protect them from predators, parasitoids and pesticides. Armored scales live beneath a waxy cover that is not attached to the adult body. Thus the cover can be removed to reveal the scale insect hidden below. Armored scales typically do not move once they begin to feed and do not produce honeydew. In contrast, soft scales secrete a waxy layer over themselves that cannot be separated from their body. Soft scales also excrete sugary honeydew and may move from branches to leaves during their life cycle. Black sooty mold fungus is often associated with this honeydew.

Armored scale are typically small and inconspicuous. The protective covers often blend well with plant bark so populations may become very large before being detected or a plant shows noticeable damage. Therefore, scouting is especially important on plant species that are frequently infested by armored scale. Armored scale damages plants by extracting plant fluids. This can reduce plant growth and vigor. Common symptoms of infestation include premature leaf drop and branch dieback (Fig. 1). Infestations are common on trees stressed by physical damage, drought, or improper planting. Heavy infestations might kill a tree or shrub.

dying euonymus shrub

 

 Fig. 1. Euonymus bush infested with euonymus scale showing, yellowing, leaf drop, and branch dieback.   infested maple tree Fig. 2. Maple tree infested with gloomy scale showing leaf drop and branch dieback.

Common Armored scale

Euonymus scale – Look for euonymus scale on leaves and stems of Euonymus spp. but also pachysandra, hollies, and camellias.  The female scale cover is oyster-shaped, gray, and 1-1.5 mm long.  Males are white (0.75 mm) with no cover and 2 visible wings (Fig. 3).  In North Carolina there are three well synchronized generations per year with first crawlers emerging in early May then in 6-8 week intervals.  Typical damage symptoms include yellow spots on the upper side of leaves where scales and premature leaf drop(Fig. 4).
euonymus scale on leaf

Fig. 3. Male and female euonymus scale on the underside of a euonymus leaf.

 splotching on leaf Fig. 4. Yellow spots from euonymus scale feeding.

 

Tea scale – Tea scale is most common living on the underside of camellia and Japanese holly leaves.  Female tea scale covers are brown and boat-shaped.  Males are soft and white with a ridge down the back.  Hatching occurs throughout the year rather than in discrete generations.

tea scale

 

 

Fig 5. Adult male and female tea scale covers.

 splotches on camelia leaf

 

 

Fig. 6. Yellow blotchy damage on the top-side of a camellia leaf from scale feeding below.

 

Gloomy scale – Gloomy scale lives on the trunk and branches of maple trees.  They are convex, gray, and occur in dense patches.  Mature female covers have a dark spot (shed skin) just off center whereas male covers have a spot near the cover edge.  They have one generation per year with crawlers active throughout June, July, and August. This complicates management by making it hard to target crawlers with insecticides over a broader period. Damaged trees become unhealthy looking with sparse canopies and branch dieback.
gloomy scale crawlers

 

 

 

Fig. 7. Crawlers under gloomy scale cover.

 female gloomy scale Fig. 8. Adult female gloomy scale  with convex cover and settled 2nd instar scales with small circular covers.

 

Obscure scale – Obscure scale is most common on the trunk and branches of oak and hickory trees.  It is relatively flat and gray.  There is one generation per year. Crawlers are active for a variable and extended period that starts in July, although on white oak crawlers emerge in August.
underside of obscure scale Fig. 9. Adult female obscure scale under cover on pin oak branch. female obscure scale Fig. 10. Adult female obscure scale.

 

Juniper scale – Juniper scale is common on junipers, cypress, false cypress, and arborvitae where it feeds on stems and leaves of the host.  Adult scale covers are circular and white with a yellow center 1-2 mm in diameter.  There is one generation per year with crawlers present in May or June.  Damage includes needles that are off color and may turn brown or die.
juniper scale on juniper

 

Fig. 11. Adult female juniper scale on juniper needles.

 

 

    

 

Armored Scale Management

Scouting for scale should be done in early spring so scale populations can be monitored for crawler activity.  Many natural enemies help suppress scale abundance and damage.  If evidence of predation (scales chewed open) and parasitism (circular holes in scale covers) are present you may decide to monitor the populations rather than treat with insecticides or use a product with less impact on the beneficials.  When insecticide applications become necessary, dormant oil applications can be made in winter to kill scale on trunks and branches.  Otherwise, target the crawler stage with horticultural oil or a systemic insecticide. 

Table 1. Insecticides labeled for use on ornamental plants to manage soft scale in greenhouses (G), nurseries (N), and landscapes (L).
*Suitable for homeowner use.

Active ingredient

Trade name

Labeled location

Activity

 Signal word

 IRAC
MOA
group

Compatible with
beneficials
acephate
Orthene, *Orthenex
G, N, L
Contact + Translaminar
Caution
1B
No

acetamiprid

TriStar

G, N, L

Translaminar Systemic

Caution

4A

Yes

buprofezin

Talus

G, N

Contact

Caution

16

Yes

dinotefuran

Safari, *GreenLight Tree and Shrub with Safari

G, N, L, I

Systemic

Caution

4A

Yes

horticultural oil

*many

G, N, L, I

Contact

Warning

-

Yes

insecticidal soap

*many

G, N, L, I

Contact

Warning

-

Yes

pyriproxyfen

Distance

G, N, L

Translaminar

Caution

7C

Yes

 

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. © 2001 NC Cooperative Extension Service

For assistance, contact your county North Carolina Cooperative Extension Service agent.

Other Resources

Web page last reviewed January, 2011 by the webperson.